Fine mesh screening of midden material and the recovery of fish bone: The development of flotation and deflocculation techniques for an efficient and effective procedure

Geoarchaeology: An International Journal, Vol. 15, No. 1, 21–41 (2000)� 2000 John Wiley & Sons, Inc. CCC 0883-6353/00/010021-21

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Fine Mesh Screening of Midden Material

and the Recovery of Fish Bone: The

Development of Flotation and

Deflocculation Techniques for an

Efficient and Effective Procedure

Anne Ross1 and Ryan Duffy2

1Department of Anthropology and Sociology and School of Natural and Rural

Systems Management, University of Queensland, St. Lucia, Queensland 4072,

Australia2School of Natural and Rural Systems Management, University of Queensland,

Gatton College, Queensland 4345, Australia

The absence of fish remains in archaeological sites in Moreton Bay, southeast Queensland,Australia, may be a function of recovery techniques, rather than a reflection of resourcepaucity and late onset of occupation, as has been posited in archaeological literature. Anexcavation on Peel Island in Moreton Bay was devised, in part, to test this proposition, anda 1-mm mesh screen was used to enhance recovery. But sorting this fine fraction took 20 h.In this article we outline experiments to find a more efficient and effective technique forsieving and sorting fine fraction archaeological deposits, using methods borrowed from soilscience. We show how sorting time can be reduced to 2 h 30 min per 100 g sample and arguethat the vast increase in knowledge about the site occurring as a result of using the very finemesh sieve warrants the continued application of these laboratory methods. � 2000 JohnWiley & Sons, Inc.

INTRODUCTION

Based on the paucity of fish bone remains discovered in shell midden depositswithin Moreton Bay, southeast Queensland, Walters (1989, 1992) has argued thata significant fishery was not introduced in this region prior to ca. 2000 B.P. andthat consequently occupation was limited and sparse until that date. In fact, ar-chaeological evidence indicates that occupation of the region was sparse until1200–1000 B.P., reflecting a late exploitation of all marine resources until that time(Ulm, 1995, 1998). This conflicts with Aboriginal oral history which states thatpeople have been living within the region known as Quandamooka (Moreton Bayand associated islands—see Figure 1) since the Dreaming. Throughout this time,fishing and shell fish harvesting have been important cultural activities in Quan-damooka society (Ross and Quandamooka, 1996a, 1996b).

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Figure 1. Map of Quandamooka (Moreton Bay), southeast Queensland, showing the location of PeelIsland.

Archaeological evidence confirms a long occupation history for the region. AtWallen Wallen Creek, on the western coast of North Stradbroke Island, Robert Nealexcavated a site which demonstrates that marine exploitation (although not fishing)has been the dominant subsistence activity at the site from 20,000 B.P. to thepresent (Neal and Stock, 1986:621). Evidence from other archaeological sites onNorth Stradbroke Island, and elsewhere within Moreton Bay, indicates that theAboriginal subsistence economy was based principally on marine resource har-vesting, at least during the late Holocene (Hall and Robins, 1984; Ulm, 1995; Walters,1989, 1992).

Although there is evidence for shellfish gathering at these and other more recentsites, evidence for fishing is temporally limited. The few sites in Moreton Bay that

FINE MESH SCREENING OF MIDDEN MATERIAL AND RECOVERY OF FISH BONE

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date to earlier than 2000 B.P. have very few fish remains (Ulm, 1995:88 [Table 6]).In fact, of the entire 59 excavated shell midden sites in the Bay, only 20 have yieldedany fish bones at all, and even then the quantities are small. Few sites have fishbone more than 1000 years old, NISPs are generally fewer than 1000, and totalweight of fish bone recovered is less than 50 g per site. Walters (1987, 1992) andUlm (1995) have both demonstrated that the absence of fish bone from sites inMoreton Bay cannot be explained by taphonomic processes, including preserva-tion.

Walters (1987, 1989, 1992) argues that fishing was simply not present in MoretonBay sites prior to ca. 2000 B.P. and was not a significant component of subsistencein Moreton Bay prior to ca. 1000 B.P. (see also Ulm, 1995:88 [Table 6]). Accordingto Walters, the coastal ecology of this region, dominated by the “wallum” ecosys-tem, was depauperate and could not provide a subsistence economy to support areasonably large human population. Terrestrial fauna and shellfish communitiesalone were insufficient to support a permanent population (Walters 1989, 1992; seealso Ulm, 1995:12–13). Coastal occupation was predicated upon the presence of asignificant marine fishery, and, until this was established, there was little occupa-tion of Moreton Bay of any kind (Walters, 1987:216).

In 1995, Ulm challenged Walters’ model of a lag in settlement and exploitationof the Moreton Bay coasts. Ulm (1995:105) argued that one of the problems withthe data upon which the model is based is the accuracy of recovery techniquesused. With the exception of a 2 mm sieve that was used at excavations on St. HelenaIsland (Alfredson, 1984), 3 mm sieves (i.e., sieves with a 2 mm mesh and 2.8 mmhypotenuse) have been universally used on all excavations within Moreton Bay(Ulm, 1995:68–69 [Table 4]).

Ulm (1995) argued that the absence of fish bone could be due to the commonuse of 3 mm sieves in most excavations in the Moreton Bay region. He pointed outthat fish bone is very fragile and may become fragmented, especially when burnt,and hence is able to pass through a 3 mm sieve. He went on to predict that smallersieve sizes would recover significant quantities of fish bone.

Excavation and analysis of a large shell midden—the Lazaret Midden (see Figure2)—on Peel Island in Moreton Bay was designed, in part, to test Ulm’s proposal.The research and experiments discussed in this article began as an effort to answerthis significant question in Australian prehistory, but ended up having broaderimplications for the recovery and sorting of materials from archaeological sitesgenerally.

PROBLEM AND AIMS

The excavation and analysis of the Lazaret Midden was undertaken by Ross andmembers of the Quandamooka Aboriginal Land Council’s Cultural Resources Man-agement (CRM) Team. Unlike previous excavations, the excavators used a 1 mmEndicott sieve (1 mm �1 mm mesh with maximum diagonal length of just over1.4 mm) to sieve the deposit which passed through the 3 mm screens in an effort

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Figure 2. Map of Peel Island, showing location of the Lazaret Midden and the three excavation locations.



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to increase the retrieval of fish bone. Although the results from this exercise dem-onstrated that fish bone is indeed present throughout the site (see Discussion later),the value of the exercise was being jeopardized by the length of time it took to sortjust 100 g of this fine material. Using normal dry sieving techniques, a 100 g sampletook an average of 20 h to sort. Even after wet sieving, sorting time was unac-ceptably long at over 10 h. This was a problem for us not only in terms of timetaken. Members of the CRM Team who undertake sorting travel from North Strad-broke Island to the University 1 or 2 days per week. With 4 h per day in travel time,this often meant that different members of the Team were sorting the one sampleover 2 or sometimes 3 weeks. This often lead to confusion and errors.

A new sieving technique had to be devised that would:

1. reduce the time it takes to sort 100g of the archaeological sediments, and2. increase the recovery of bone.

There are a number of techniques commonly used by archaeologists and soil sci-entists to increase the efficiency and effectiveness of sorting and analyzing archae-ological materials and soils. In consultation with the Quandamooka community wedetermined that the technique that would be most suitable to the Lazaret Middenexcavation would need to be one that would meet a number of criteria:

● The technique must be inexpensive and the chemicals must be readily avail-able.

● It must be able to sort 100 g of archaeological material in a single working day(i.e., 6 h or less).

● It must use chemicals, which are non-toxic and not flammable.● It must not damage the materials which are floated; hence, it must be neither

extremely acidic nor basic.● The procedure must be easy to implement and repeat.● It must yield at least as much bone as the manual sieving techniques.● It must be a technique acceptable to the Quandamooka Aboriginal community.

The new technique employed three principal elements:

1. Recovery, based on literature review;2. Chemical separation, based on experimental procedures;3. Deflocculation of soil matrix, based on experimental procedures.

We discuss each of these methods and their results in turn.

METHODS AND RESULTS FOR RECOVERY TECHNIQUES

There has been considerable debate in the archaeological literature of the past3 decades regarding the most appropriate sieve sizes that should be used for themost effective retrieval of faunal remains. In 1969, Thomas conducted a series ofexperiments, which demonstrated the amount of bone that is lost through the rela-tively large mesh sieves regularly used on archaeological sites. He found that the

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larger the screen size used, the more underrepresented are the bones of smallanimals such as rodents and fish. He concluded that “one should always excavatewith a maximum recovery screen” but went on to acknowledge that “the realitiesof archaeological fieldwork seem to preclude such exacting and time-consumingprocedures” (Thomas, 1969:399).

Thomas’ findings have been duplicated and discussed by a number of researchers(e.g., Barker, 1975; Casteel, 1970, 1975; Dye, 1994; Gordon, 1993, 1994; James, 1997;Payne, 1975; Shaffer, 1992; Shaffer and Sanchez, 1994). All of these authors docu-ment that the larger screen sizes underrepresent small animals, especially fish bone.For example, Gordon (1993:453) demonstrated that:

The larger screen fractions inch [12 mm], inch [6 mm]) do not recover, or1 1( ⁄2 ⁄4may under-represent, smaller taxa (e.g. rodents, smaller birds, and fishes) andsmaller skeletal elements (e.g. otoliths, . . .).

It is undeniable that many small bones, particularly fish bones, regularly passthrough 3 mm screens. James (1997), for example, is one of many to demonstratethis phenomenon. He compared the results derived from sieving material throughthree different screen sizes: 6 mm 3 mm (1/8 in.) and 1.5 mm (1/16 in.). He1( ⁄4 in.),found that fish bone in particular is greatly affected by the screen size chosen: “90%of fish remains at sites may be lost through in. [6mm] [screens]” (James, 1997:1⁄4385). In fact, in Thomas’ (1969) excavation of rockshelter sites in Nevada, fish boneswere only recovered in the 1.5 mm sieve (James, 1997:386). Furthermore, it wasonly by using a 1.5 mm sieve that the use of fish in Hohokam sites in the UnitedStates was documented at all (James, 1997:389, 395).

Barker (1975:63) argued that larger screen sizes only give information about thepresence of bone in archaeological sites, not the absence of particular species.When screen sizes larger than 3 mm are used in excavations—and 6 mm 1( ⁄4 in.)screens are the “industry standard” in North America (James, 1997:385)—it is clearthat the interpretation of the dietary range of the users of the site is likely to beseriously inaccurate. This is particularly the case with fish bones.

Experimental work by Colley (1987) has shown that fine fish spines will be amongthe first bones lost from a fish during the cooking process:

A very high proportion of bones found in the hearth [as opposed to being retainedwithin the flesh of the fish] were highly fragmented fin rays (75% of dorsal finrays, and 85.7% of other fin rays). (Colley, 1987:4)

Such fine bones require a 1mm mesh sieve for effective retrieval (Colley, 1987:3).Given the abundant evidence of the value of the 1.5 mm (1/16 in.) sieve for the

retrieval of small animals and fish remains from archaeological sites, why is theresuch a reluctance on the part of archaeologists to use small sieves? The mainproblem is the amount of time it takes to sort the archaeological material retainedin the sieve. Shaffer (1992:129), for instance, argues that the use of 1/16 in. (1.5 mm)sieves “can result in a 500 percent increase in screening time relative to use of



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[6 mm] screens” and that such an expense makes use of anything smaller than1⁄4�6mm inefficient.

Consequently, although the effectiveness of the small sieve is unarguable, es-pecially in sites where fish remains are likely to be part of the deposit, its efficiencyis problematic. If sorting time could be reduced, then both the effectiveness andefficiency of using a fine mesh sieve would make the technique more acceptable.

EXPERIMENTAL METHODS AND RESULTS FOR FLOTATION

The bulk of the experimental work relating to chemical separation of sedimentsand deflocculation of soil matrix (see later) was undertaken by Duffy (as an In-dustrial Placement project for his Bachelor of Applied Science [Natural Systemsand Wildlife Management] degree) in four stages:

1. Background literature review to determine the applicability of the techniqueto the Lazaret Midden material at a theoretical level.

2. A 10 g experimental sample from Pit A, XU15 (a pre-1000 B.P. unit of theLazaret Midden) was prepared and sorted using each of the chosen tech-niques.

3. From these experiments the most successful techniques were selected andthen applied to 100 g samples. The time it took to sort each sample was thenrecorded.

4. The final step of the project was to identify the most successful technique, interms of the sorting time, the recovery of material, and expense.

Before experiments were performed to measure the efficiency and effectiveness ofchemical flotation and deflocculation, details of dry sieving alone were recordedto provide a control sample.

Dry Sieve Procedure and Results

Dry sieving of sediments required no preparation of the sample at all. All of thesediments that were contained within the 1mm fraction had previously passedthrough a 3 mm mesh sieve. The initial stage of a dry sieve involved sieving 100 gof material that had passed through the 3 mm sieve into two size classes to isolateall the material larger than or equal to 1.5 mm. The two implements used were a1 mm Endicott sieve (hypotenuse 1.4 mm), and a nonscreen Endicott base. Theseimplements were consistently used with all other experiments to isolate the frac-tion retained in the 1 mm Endicott sieve, that is, all material between 3 mm and1.5 mm in size. All the material that passed through the 1mm Endicott sieve wascaught in the base, and bagged as residue. About 60% of a 100 g sample containedmaterial that would pass through a 1 mm mesh, therefore only 40 g of material wassorted. Sorting was conducted under a maggylamp using a pair of tweezers. Thesorted material was then bagged according to the specific class of archaeologicalsediments (e.g., shell, bone, humus, charcoal, insect case, pebble, coral, and soil).Sorting took 20 h.

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The dry sieving process was the main sorting technique used previously to sortthe archaeological sediments from Peel Island. The quantities of material withineach specific class that had been sorted using the dry sieving process would act asa future reference point for comparing the recovery rates of other techniquestrialed (see Table I).

Chemical Separation

For decades archaeologists have used a variety of flotation techniques for therecovery of charcoal, plant remains, and other material from excavated sites. Thebasic concept of flotation involves immersing archaeological sediments in a liquid.Material with a specific gravity less than the liquid will float to the top of the liquid,the “light fraction,” while the rest of the sediments will sink to the bottom of thesolution, the “heavy fraction.” In most cases the light fraction consists of charcoaland plant remains, while the heavy fraction contains bone, shell, lithics, and othermaterials.

The advantages of using flotation procedures for the recovery of archaeologicalsediments are as follows:

1. Flotation may overcome sampling biases. For example, Struever (1968) onlydiscovered the presence of charred seed remains in excavated material afterthe flotation process had been applied: “Without this simple water-flotationtechnique these seeds would have been lost, not withstanding the fact thatthe fill had been carefully hand trowelled from the pit” (Struever, 1968:353).

2. Flotation divides the sediments into two separate material classes, the lightand heavy fractions. This reduces the chance of misidentification. Materialsuch as charcoal and soil aggregates, or fish bone and certain organic matter,are sometimes hard to differentiate while sorting. Because soil will remain inthe heavy fraction and most of the charcoal will float (the same is true withfish bone and organic matter) sorting becomes significantly easier. This mayin turn decrease the sorting time because less effort is spent identifying spe-cific archaeological sediments.

Chemical flotation is one of the main flotation techniques used in archaeology. Theconcept involves manipulating the specific gravity of a given solution to float dif-ferent quantities and types of material. The solution used in flotation needs to havea specific gravity which lies between that of the two sediment classes needing tobe separated. For example, charcoal has a specific gravity of approximately 0.62while bone is 2.1 (Bodner and Rowlett, 1980:113). Therefore a solution with a spe-cific gravity in between 0.62 and 2.1 would separate these two material classes.Charcoal would comprise the light fraction and bone the heavy fraction.

Water has an approximate specific gravity of 1.0; hence in theory it could sepa-rate charcoal and bone. It becomes impractical, however, to use water when therequired specific gravity is either much greater or much less than 1.0. To modifythe specific gravity of water, certain chemical solutions can be used.

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Table I. Summary of the results of sieving experiments using the four main techniques.

Technique

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Shell(g)

Bone(g)

Humus(g)

Charcoal(g)

Other(g)

Lostb

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Dry sieve 19.4 69.8 8.8 17.6 0.1 0.1 0.3 0.6 2.7 Time taken makes sorting inefficient.Large quantities of soil retained insieve. Few fine particles were lost

Wet sieve (wateronly)

9.2 67.3 5.2 16.7 0.1 0.0 0.2 0.5 10.0 Time taken is an improvement. In-crease in “lost” material indicatessome finer particles washed downthe sink. Nevertheless, largeamounts of soil flocculates still re-tained in sieve

Sugar flotation 7.0 66.5 5.3 19.1 0.2 0.2 0.6 0.6 7.5 Sort time further improved. Lightfraction amounts increased, andno soil or shell in light fraction.Amount of soil flocculates re-tained in sieve still makes sortingslow

Sugar flotation plussodium bicar-bonate defloccu-lation

2.5 66.7 0.1 17.9 0.3 0.2 0.7 0.8 13.5 Vast improvement in sorting time,largely a result of deflocculationof almost all soil particles. In-crease in “lost” fraction furtheremphasises value of defloccula-tion. Increased quantity of boneemphasises easier identification ofcultural elements

a“Residue” is all particles which fall through the 1 mm Endicott sieve to be caught in the base sieve. “Other” includes coral, pebbles, and insect casings.b“Lost” means the very fine material that washes down the sink or is not caught in any of the sieves or other traps.

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A chemical solution with a specific gravity greater than 1.0, but less than 2.1,would have a greater chance of separating 100% of the charcoal from the bone inthe sample. Inevitably not all of the material within the light fraction will float. Themere use of flotation does not ensure the recovery of all possible artefacts (Wagner,1982:127). Some material may become waterlogged or be too large to float. But asolution with a higher specific gravity would have a greater chance of recoveringalmost all the sediments that are contained within the light fraction. Therefore, asolution with a specific gravity of 1.5 would float more charcoal than would water.

Flotation alone will not guarantee the separation of all archaeological sediments,but it may be an effective technique to employ when looking to reduce the sortingtime of the fine fraction from Peel Island.

Limitations of Chemical Flotation

Chemical flotation has been used successfully by many archaeologists in the past.Struever used zinc-chloride to separate bone from plant remains. This resulted inan almost 100% separation of these two particular types of material (Bodner andRowlett, 1980:111). Nevertheless, although Struever was able to obtain exceptionalresults, zinc-chloride is not only expensive, it is highly caustic (Kidder, 1997:40).Another drawback with Struever’s technique is that zinc-chloride is hydroscopic;hence material immersed in such a solution needs to be thoroughly rinsed or it willnot dry.

Bodner and Rowlett used “ferric sulphate to separate bone from gravel, andeither ethyl ether or acetone for separating seeds from charcoal” (Bodner andRowlett, 1980:114). This technique is more cost effective than Struever’s and didnot require the use of caustic chemicals. The chemical solutions are commonlyavailable and relatively inexpensive, “but ethyl ether and acetone are highly flam-mable, while ferric sulfate is hydroscopic” (Kidder, 1997:40).

The use of toxic chemicals within the scope of the Peel Island project could notonly adversely effect the archaeological sediments themselves, it could also haveadverse cultural ramifications. The Quandamooka community has indicated a de-sire to have all the midden material returned to the site once analysis is complete.To return material affected by toxic chemicals to an island in a Marine NationalPark is unacceptable on both cultural and environmental grounds. Members of theQuandamooka CRM Team indicated that they would prefer it if toxic chemicalswere not used on their cultural artefacts.

Flotation Apparatuses

Chemical flotation is sometimes accompanied by a flotation apparatus developedto sort bulk quantities of excavated material either on site or in the laboratory.These include SMAP machines (Williams, 1973), or froth flotation devices, siphons(Gumerman and Umemoto, 1987:330), and seed blowers (Ramenofsky et al., 1986).

The majority of literature relating to flotation processes is dedicated to systemsthat can sort bulk quantities of soil, usually on site (Diamant, 1979; French, 1971;



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Jarman et al., 1972; Limp, 1974; Pearsall, 1989; Watson, 1976; Williams, 1973). Theydiffer from manual flotation systems because they are machine assisted and henceincrease in complexity when compared to manual systems.

Machine-assisted flotation apparatuses used to sort bulk quantities of materialwere not considered to be appropriate for the unique circumstances of the PeelIsland project, where material will only be sorted in 100 g lots. Restrictions inlaboratory space meant that permanent or even temporary erection of the equip-ment was not possible.

The siphon technique, as described by Gumerman and Umemoto (1987:330), wasalso not considered likely to reduce the sorting time by any significant margin.Even though this technique could extract most, if not all, the charcoal that did notfloat and the fish bone, it would also extract a lot of the shell and aggregated soilthat make up the bulk of the heavy fraction. Consequently, it would not sufficientlyseparate materials to improve sorting time.

The seed blower technique (Ramenofsky et al., 1986) was also not feasible forthe Peel Island sorting because of the inability to gain regular access to the nec-essary equipment.

Flotation Experiments

Flotation without Chemicals

Initial experiments dealt with flotation in water without chemicals. The samplewas placed in a 1 mm Endicott sieve, nested above an Endicott base to catch allmaterial that passed through the sieve. A tap provided a constant flow of water.The light fraction was skimmed off the surface using a plastic spoon. The lightfraction, the material retained in the sieve, and the residue retained in the tray werelaid out to dry on paper towels in a drying rack.

The next phase of this experiment involved sorting both the heavy and lightfractions into their separate material classes.

Results of Flotation without Chemicals

There was little difference between the heavy and light fractions using this tech-nique. The light fraction contained mollusc shell, charcoal, humus, and insect cases,while the heavy fraction contained mollusc shell, charcoal, small quantities of hu-mus and insect cases, coral, bone, pebbles, and a very large quantity of soil aggre-gates. The main difference between this technique and the dry sieving control sam-ple was that a lot of fine sediment had been washed out of the heavy fraction whichmade this sorting process significantly easier and less time consuming. It tookbetween 9 and 12 h to sort a 100 g sample, which was a reduction of approximately50% when compared to the control dry sieving process.

Separating the archaeological sediments into two material classes (light andheavy) is mostly credited for reducing the time it took to sort the material. This isbecause significantly less time was spent trying to differentiate between soil and

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charcoal, or humus and bone.This technique and the dry sieving control recoveredsimilar amounts of bone.

Chemical Flotation

When using chemical flotation a number of questions needed to be resolved toensure the procedure was efficient and effective.

1. What chemical solution would produce the best separation of the archaeolog-ical sediments into two material classes?

2. What is the minimum concentration and volume of a solution that would pro-duce acceptable results? Concentration and volume are the two key factorsthat determine the specific gravity of the solution. Alternatively this questioncould be reworded to say: What would be the minimum specific gravity thatwould produce as close to 100% separation of the sediments into two materialclasses?

3. What is the most efficient and effective flotation procedure?4. Does the cost of the flotation solution and procedure justify the results ob-

tained?5. Are the results consistent?6. Does the chosen chemical meet all the specific constraints outlined in the

aims?

We identified three different types of chemical solutions as being appropriate forthe Peel Island project in the light of the selection criteria. They were salt water,sugar water, and cooking oil (canola).

Salt: Lange and Carty (1975) used salt water (sea water) flotation in conjunctionwith their research on the northwestern coast of Costa Rica. Salt water was usedto float mollusc shells, small bones, fish scales, charcoal and seeds. Greater quan-tities of material were retrieved in the light fraction due to salt flotation whencompared to fresh water flotation. “Preliminary observations indicate the weightand frequency of light fraction materials is increased at least by a factor of two insalt water flotation” (Lange and Carty, 1975:122). More residue is retrieved in thelight fraction after salt water flotation because the solution has a higher specificgravity than fresh water. Therefore, saltwater flotation would have a greater chanceof achieving 100% separation of the light fraction from the heavy fraction thanwould tap water.

Sugar: Sugar flotation has been used by limnologists and fisheries scientists toseparate benthic organisms from sediments. Kidder (1997) used this technique inan archaeological context to retrieve carbonized plant remains from sediments.“One gallon [approx. 3.8 liters] of tap water was mixed with 2.5 lb [approx. 1.1 kg]of sugar to form a solution with an approximate specific gravity of 1.11. . . ; thissolution is capable of floating charcoal and seeds” (Kidder, 1997:42). The advantageof sugar flotation is that it is inexpensive, does not carry any environmental threat,and does not damage the material which is immersed in the solution.



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Oil: Oil is a flotation technique used in some engineering procedures to floatlighter impurities in soil mixtures. We know of no previous applications of thistechnique to archaeological situations.

Procedures Used in Chemical Flotation Experiments

Before being used in flotation experiments, samples were always presieved (dry)using the same methods described for the dry sieving control process.

Various quantities of raw sugar and salt were poured into water and stirred untildissolved. The amount of sugar or salt added to 400 ml of water ranged from 20 gto 250 g. When oil was tested, it was added to 400 ml of water until there was alayer approximately 3–5 cm thick. The type of oil used was canola oil. No proce-dure was undertaken to determine the best type of oil; canola was just the cheapestavailable.

The presieved 10 g sample was poured into a beaker containing a solutionof water and the chemical being tested. The solution was then poured out of the500 ml beaker through a fish tank net, with a mesh size of approximately 0.25 mm,and into another container. The fish tank net captured any material that floated(light fraction). When the material in the heavy fraction approached the lip of thebeaker, pouring ceased. The solution that had been caught in the second containerwas poured back into the 500 ml beaker, and the whole process was repeated. Theprocess had to be repeated several times to ensure that any charcoal or other lightfraction material which had attached itself to the side of the 500 ml beaker wasrinsed out. The material caught in the fish net was finally rinsed with plain waterand laid out to dry on paper toweling in a drying rack.

Results of Chemical Flotation Experiments

Sugar and salt were the best additives; there was little difference between thetwo. Oil flotation was the least successful method. It coated all the sediments in afine film of oil that was very hard to rinse off. Moreover, the quantity of materialfloated in oil was similar to that which had been achieved using plain water.

The approximate specific gravity of a saturated solution of sugar or salt is 1.66or 1.55, respectively. More sugar than salt could be dissolved in water before thesolution reached its saturation point (260 g of sugar could be dissolved in 300 mlof water as compared to 120 g of salt). When equal amounts of salt and sugar wereadded to 400 ml of water, sugar would float more material.

Further experimentation showed that it was not possible to use the maximumconcentration of sugar. Using such a concentrated solution produced a sugar ex-tract in the light fraction after flotation. The extract had to be carefully picked outof the light fraction, which made sorting more time consuming. The sugar extractdid not appear in less concentrated solutions.

We determined, therefore, that the best results for flotation came from using asugar solution at a concentration of 80 g in 400 ml of water. Although salt producedsimilar results, sugar, with its higher specific gravity, produced slightly better re-

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sults. Another problem with salt is that this chemical cannot be used in conjunctionwith sodium hexametaphosphate, a deflocculation agent, which is an importantpart of the experiments in deflocculation described later.

Sorting a 100 g sample after sugar flotation produced a noticeable differencebetween the light and heavy fractions. The light fraction contained humus andcharcoal, while the heavy fraction contained small quantities of humus and char-coal, as well as shell, bone, soil aggregates, coral, and other “heavy” materials.Sorting time was further reduced to 7 h, but the presence of soil floccules in theheavy fraction was still impeding the sorting time.

Deflocculation of Soil Matrix

Flocculation occurs when individual soil particles attach together into smallclumps or floccules (Brady, 1990:586). Deflocculation, which disperses soil aggre-gates or clumps, has been used by many archaeologists to disperse problem soils,especially those with a high clay content.

Deflocculation can improve flotation results. When the clay content is highenough to impede soil dispersion in water, flotation can be very difficult and un-productive (Pearsall, 1989:85). If the soil does not disperse, certain materials whichhave been locked up in the soil aggregates, such as organic matter and shell, maynot be released for flotation or later sorting.

Deflocculation can also be used as a pretreatment before fine sieving because itwill disperse aggregates or clumps of soil which would have otherwise not passedthrough the mesh.

Flocculation is influenced by a number of factors. Soil colloids that absorb ionssuch as calcium, magnesium, or aluminium, encourage flocculation. On the otherhand, ions such as sodium encourage dispersion and hinder the formation of ag-gregates (Brady, 1990:111).

Soil dispersion is conducted within a liquid solution, usually a mixture of waterand a chemical with a high concentration of sodium. Examples of chemicals thathave been used to deflocculate soil are as follows:

● sodium hexametaphosphate—commercially marketed as a type of water soft-ener known as calgon (Keeley, 1978:180; Pearsall, 1989:85);

● sodium bicarbonate—baking soda (Keeley, 1978:180; Kidder, 1997:41);● mix of ammonia and sodium bicarbonate (Pearsall, 1989:85);● hydrogen peroxide (Keeley, 1978:180; Pearsall, 1989:85).

Limitations of Deflocculation

Samples that have been left to soak in a chemical solution to aid deflocculationmay become waterlogged (Pearsall, 1989:86). Charcoal and other sediments tendto sink after being immersed in a solution for a long duration. Thus the amount ofmaterial recovered in the light fraction may be significantly reduced due to defloc-culation procedures. The chemical solution used for deflocculation may also dam-age archaeological materials. Therefore, one must be sure that the recovery rate



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of archaeological material before deflocculation was used is compatible with therecovery rate after deflocculation.

The following is a detailed outline of the experiments undertaken, the proceduresused, and the results achieved.

Deflocculation Experiments

Procedures Used in Deflocculation Experiments

The procedure undertaken to deflocculate a sample was similar to the flotationprocedure. Smaller samples (10 g) were initially used, and all samples were pre-sieved. Only the 1 mm fraction was used in the deflocculation process. A prede-termined quantity of either sodium hexametaphosphate or sodium bicarbonate wasadded to hot water. Hot water decreased the time it took to dissolve the defloc-culant and also improved deflocculation results. Quantities of sodium hexameta-phosphate or sodium bicarbonate mixed with 400 ml of water ranged from 25 to90 g.

Ideally the best results would be achieved when a solution was completely sat-urated with either of the deflocculating agents, but this was not necessary. Ade-quate results were obtained using 40–70 g of the agent, which is much less thanthat which would be needed to saturate a solution.

Two deflocculating techniques were tested on the Peel Island material; soakingthe material in a deflocculating agent and agitating the material:

1. Soaking. After the deflocculant had completely dissolved, the midden samplewas left to soak in the solution for varying durations, which ranged from 1 to16 h. The solution was then thoroughly rinsed before being sieved and thendried.

2. Agitating. After the deflocculant had completely dissolved, the midden sam-ple was left to soak in the solution for approximately 5 min. The majority ofthe solution was then poured carefully out of the beaker until only a thin filmcovered the material at the bottom of the beaker. The midden material wasthen agitated for 1 min by rotating the beaker in a circular motion. The frictioncaused by shell, pebble and coral fragments, etc. aided deflocculation of thesoil. The whole process was repeated several times until it was visibly evidentthat most, if not all, of the soil aggregates had dispersed.

Results of Deflocculation Experiments

Soaking the midden material in a solution of sodium hexametaphosphate for16 h deflocculated all but 0.3 g of soil aggregates, while soaking in sodium bicar-bonate deflocculated all but 0.4 g of soil aggregates. When compared to the originaldry sort (which left 8.8 g of soil aggregate), the quantity of soil aggregates beingsorted had been reduced significantly.

Even though the experimental results after sodium hexametaphosphate defloc-culation were slightly better than that which could be achieved with sodium bi-

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carbonate, the cost of the former is $A20.00 for 500 g, whereas the cost of sodiumbicarbonate, marketed as baking soda, is $A2.00 for the same quantity. Therefore,the reduced quantity of soil aggregates was not significant enough to justify theextra cost to the project if sodium hexametaphosphate was used as the primarydeflocculating agent.

The main problem with this technique is that soaking takes such a long time.When added to the time needed for drying, the time to prepare and sort a samplecould be more than 48 h. This did not suit the Quandamooka CRM Team, who cameto the laboratory only once or twice a week to do the sorting. A technique thatcould be started and completed on the one day was preferable.

Agitation proved to be a more time efficient technique, as well as being a moreeffective way to deflocculate soil aggregates. The agitation procedure broke downall but 0.1 g of soil aggregates, and the more cost efficient sodium bicarbonateproduced marginally better results than sodium hexametaphosphate. Only 40–50 g of sodium bicarbonate in 400 ml of water was needed to make the necessarysolution.

Another advantage of the agitation process was that it was also able to clean thesurface of archaeological sediments within the heavy fraction. Bone was mucheasier to identify, and as a result slightly increased quantities of bone could berecovered. A number of experiments were conducted to see if agitation had anadverse effect on bone, but there was no evidence that agitation caused any break-age or splintering of bone or other materials.

The whole process took approximately 10 min, from when the sodium bicarbon-ate solution was made until the material was laid out to dry.

RESULTS

Given the effectiveness of the flotation and deflocculation experiments in reduc-ing the preparation and sorting time for the analysis of the fine sieve fraction fromPeel Island, we undertook a number of experiments to test the effectiveness ofcombining the process into one step. Unfortunately, no combination of proceduresresulted in a satisfactory one-step process.

The best procedure utilized both sugar flotation and agitating sodium bicarbon-ate deflocculation, but not within a single solution. Table II provides the “recipe”for the most efficient and effective technique. The total time required for prepa-ration of the sample and sorting (not including drying) was 2.5 h. All but 0.1 g ofsoil aggregate was dispersed, and the retrieval of bone was slightly increased overthe control sample (0.3 g compared to 0.1 g—see Table I). The chemicals are cheap,nontoxic, and readily available from any supermarket. The technique is simple touse and easily taught to students and other laboratory volunteers. The techniquethus meets all the requirements as set out in the criteria for evaluation.

One additional advantage of the two step process is that the sugar solution couldbe re-used, as it had not been tainted by deflocculated soil. Nevertheless, there isa limit to the number of times the sugar solution could be reused. Kidder (1997:42)



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Table II. “Recipe” for chemical flotation and deflocculation procedure.

1. Dry sieve 100 g of residue through a 1 mm Endicott sieve before chemical flotation or defloccula-tion. Presieving isolates the 1 mm fraction from very fine powdery sediments that would onlycomplicate the sorting process.

2. Dissolve 80 g of sugar in 400 ml of hot water in a 500 ml beaker. Gently stir the solution until thesugar grains have completely dissolved.

3. Pour the sieved 100 g sample of residue into the sugar solution. Decant the solution through a fishtank net to capture the light fraction. When the material in the heavy fraction approaches thelip of the beaker, cease pouring. Catch the sugar solution in a second container and pour backinto the beaker.

4. Repeat step 3 three to four times to ensure that any charcoal or organic matter attached to theside of the beaker is rinsed out.

5. Rinse the material caught in the fish tank net with water and lay it out to dry on paper toweling.Keep the sugar solution in a separate container; this can be reused a further three times beforebeing replaced (i.e., sugar solution can be used on four 100 g samples).

6. Rinse the heavy fraction that is retained in the 500 ml beaker with water; then pour off as muchof the rinsing water as possible.

7. Combine 400 ml of hot water with 40 g of bicarbonate of soda in the beaker containing the heavyfraction. The bicarbonate is added to deflocculate the soil aggregates. Very gently stir the solu-tion until all the bicarbonate has completely dissolved.

8. Carefully decant the majority of solution out of the beaker and into another container. Leave athin film of the bicarbonate solution covering the heavy fraction. Agitate the residue by rotatingthe beaker in a circular motion for 30–50 s. The friction caused by fragments of residue (e.g.,shell, bone, pebbles) combined with bicarbonate deflocculates the soil.

9. Pour the decanted bicarbonate solution back into the beaker. Repeat step 8 three or four times oruntil it is visibly evident that most, if not all the soil aggregates have deflocculated. The shellfragments should be clean and white.

10. Pour off the bicarbonate solution and thoroughly rinse the residue left in the beaker. Wash theheavy fraction in a 1 mm sieve, rinsing thoroughly with tap water. Place the washed residue onpaper toweling to dry. Discard the bicarbonate solution.

pointed out that “experiments . . . suggest that a roughly seven percent reductionin recovery rate occurs among equal sized samples each time the solution is re-used.” The sugar solution should not, therefore, be reused more than three times(i.e., four uses of any one solution).

DISCUSSION

Even using the dry sieving technique, the 1 mm Endicott sieve retrieved relativelyhigh quantities of fish bone from the excavated sediments of the Lazaret Midden.Although fish bone is found in the larger screen sieves, it occurs only occasionallyand then only in small quantities (Ross et al., in prep.). On the other hand, fish bonehas consistently been recovered from the 1 mm Endicott sieves, including samplesolder than 1000 B.P. [A basal date from the site is not yet available, but a date fromapproximately half way down the stratigraphic section produced an age of 1090 �60 B.P. (Beta98032).] In each excavation unit (XU) 0.1–0.5% of the 100 g sampleanalyzed from the 1 mm sieve is bone, particularly fragmented fish spines. Almostall this fine bone is burned, and much of it is calcined. The Quandamooka

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people, both in the past and today, cook their fish over an open fire. The cookingprocess may have caused the fish bone to become more susceptible to fragmen-tation (Colley, 1987).

The total fish bone retrieved from sorting just one of the four 50 cm � 50 cmpits excavated at the Lazaret Midden is approximately 50 g. This is equal to theamount of fish bone by weight of any other single site in Moreton Bay (Ulm, 1995:88 [Table 6]), yet the 0.25 m2 so far analyzed from the Lazaret Midden is equal tothe smallest area analyzed elsewhere in the Bay (Ulm, 1995:68–69 [Table 4]). Fur-thermore, if we can assume that the 100 g sample from the 1 mm Endicott sieve isrepresentative of the remainder of the residue in each XU,1 the total fish boneweight in just one 0.25 m2 pit from Peel Island would be in excess of 150 g (includingthe fish bone from the 3 mm and 6 mm sieves). This is more than twice the weightof fish bone excavated from any other Moreton Bay site.

So the use of the small sieve at the Lazaret Midden does indeed have the potentialto change our understanding of the history of fishing in Moreton Bay. Although theevidence from one site cannot be regarded as applicable throughout the Bay, theresults of the Lazaret Midden excavation strongly suggest that fish bone may occurin other sites in Moreton Bay but that the evidence has been missed because of therecovery techniques used.

Using the new techniques of flotation and deflocculation, recovery of fish bonefrom the 1 mm Endicott sieve is slightly increased, and is much more efficient,taking only 2.5 h to sort each 100 g sample.

So just how important was fishing in Moreton Bay? If the results from the LazaretMidden are representative of the entire Bay (and there is little reason to supposeotherwise), fishing was indeed a far more significant part of Quandamooka life thanhas been recognized in previous archaeological excavations. Furthermore, fishingwas practiced both before and after 1000 B.P.

Interestingly, the more robust skeletal elements, such as skull bones, otoliths,and vertebrae, are not found as commonly as the fragmented bone. Vertebrae are

found, mostly in the 3 mm and 1 mm sieves, but the fragmented bone in the 1 mmsieve shows that fins and spines are far more plentiful. No otoliths and few skullelements have been recovered.

There may be several explanations for this phenomenon:

1. It may be due to the type of fish being eaten. The most commonly caughtspecies among the people of Quandamooka today are sea mullet, mackerel,whiting, bream, flathead, and tailor (Brian Coghill, personal communication).Many of these fish have fine bones, and even the more robust bone wouldeasily fragment with burning (Vojtech Hlinka, personal communication).

1 A 100 g sample was chosen because of the time taken to sort this material. Residue in each XU wasalways more than 2500 g. Assuming that the 100 g sample was representative of the entire bulk ofresidue, then 0.3% of the residue would mean at least 7.5 g of fish bone in each XU.



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Brian Coghill notes that the cooking process makes all the bones very frag-mentary.

2. It may be due to discard factors. If fish heads were removed at the time theywere caught, or otherwise thrown into the sea, then head bones could notenter the site. This, however, is unlikely as, according to Quandamooka tra-dition, fish are cooked whole (Brian Coghill, personal communication).

3. Dingoes (who were regulars at Aboriginal camps) and native false water ratsmay have scavenged any leftovers. Colley (1987) argues that fish fins andspines regularly end up in the fire as a result of the cooking process, so thatthese bones would be unavailable to scavengers.

Studies of the taphonomy of the fish bones in the site need to be undertaken.

CONCLUSION

Aboriginal oral history indicates that people have inhabited the Quandamookaregion since the time of the Dreaming. During this time, the majority of their sub-sistence has come from the abundant marine resources that surround them, in-cluding fish. Contrary to Aboriginal beliefs, contemporary archaeological theorieshave concluded that a significant fishery was not established within Moreton Bayprior to ca.1000 B.P. (Ulm, 1998; Walters, 1989, 1992). This conclusion is based onthe absence of fish bone at most excavated sites within Moreton Bay (Ulm, 1995).

In this article we have demonstrated that, at least at one site in Moreton Bay,use of a very fine mesh sieve—a 1 mm Endicott sieve—has revealed far highernumbers of fish bones than at any other site in Moreton Bay. Fish bone also occursin significant quantities in the pre-1000 B.P. levels of the Lazaret Midden site.

Nevertheless, even though fish bone was being retrieved by the use of the 1 mmsieve, it was taking 20 h to sort 100 g of the 1 mm material. Experiments outlinedin this article demonstrate that sorting time can be reduced to 2.5 h for a 100 gsample by using sugar flotation and deflocculation of soil aggregates in a sodiumbicarbonate solution. These techniques are cheap, nontoxic, and easy to imple-ment. The vastly increased knowledge about Aboriginal subsistence patterns whichthe 1 mm sieve provides warrants the continued use of such a fine sieve, and thepreparation methods devised to speed up the use of this sieve makes the wholeprocedure viable.

We thank the Aboriginal people of Quandamooka for permission to work on this project and to publishour findings. We particularly thank Shane and Brian Coghill for their input throughout our research. JeffEighmy, Department of Anthropology at Colorado State University, provided comments on an earlierversion of this article, and the current version is improved for his comments. Two anonymous refereesalso provided comments on the organization of our data presentation, and we thank them for theiradvice. Vojtech Hlinka (Department of Anthropology and Sociology) provided useful discussion on thefish bone taphonomy. Jon Prangnell and Jim Smith drew the figures.

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Received October 5, 1998

Accepted for publication August 24, 1999

Documents

Fine mesh screening of midden material and the recovery of fish bone: The development of flotation and deflocculation techniques for an efficient and effective procedure