The Use of Paraloid B-72 as an Adhesive: Its Application for Archaeological Ceramics andOther MaterialsAuthor(s): Stephen P. KoobSource: Studies in Conservation, Vol. 31, No. 1 (Feb., 1986), pp. 7-14Published by: International Institute for Conservation of Historic and Artistic WorksStable URL: http://www.jstor.org/stable/1505954Accessed: 21/03/2009 09:20

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THE USE OF PARALOID B-72 AS AN ADHESIVE: ITS APPLICATION FOR ARCHAEOLOGICAL CERAMICS AND OTHER MATERIALS

Stephen P. Koob

Abstract-The proper preparation and application of Paral- oid B-72 make it an excellent adhesive for archaeological ceramics and other materials. An understanding of the prin- ciples of adhesion is essential to the successful application of solvent adhesives.

1 Introduction

The need for a stable and suitable general purpose adhesive for archaeological ceramics has long been an issue of controversy and concern to the conservator. Paraloid B-72 is one of the most stable thermoplastic resins available to the conservator, but until recently has only been considered suitable as a consolidant. The reasons for this exclusion can be attributed, in part, to the traditional easy-to-use commercially pre- pared adhesives (based primarily on cellulose nitrate or polyvinyl acetate), as well as the difficulties in manipulating the workability and application of the acrylic resins as adhesives.

Some of the criticisms often cited against the use of Paraloid B-72 and other acrylic resins include string- iness, poor adhesion, low tack and long setting-times. Although these criticisms at first may seem to be justified, a closer examination and understanding of the problems indicate that all of these properties can be controlled by proper preparation and application.

2 Properties of Paraloid B-72 and its suitability as an adhesive

Table 1 Physical and chemical properties of Paraloid B-72

Glass transition temperature (Tg) 40?C Ultimate Tukon hardness (KHN) 10-11 Sward rocker hardness 80 Pencil hardness H Solubility parameter 9.3 Viscosity (cps at 25?C, 40% solids solution)

in acetone 200 in toluene 590

The chemical properties and stability of B-72 are well known [1, 2] and it displays the properties most desired of a general-purpose adhesive: stability (resistance to oxidation, light, hydrolysis and mod-

Received 30 April 1985

erate heat), transparency, mechanical resistance and reversibility. The strength of B-72 is well suited to an adhesive, and it is compatible with a wide variety of materials. Rohm and Haas [2] recommends B-72 for its excellent adhesion to glass, and for coatings over plastics, metals, wood, masonry and cloth, as well as for barrier and top coats, and finishings for metals (furniture, cabinets and automotive lacquers). The physical and chemical properties of the resin are listed in Table 1 [1, 2].

Figure 1 Failure of cellulose nitrate adhesive and damage to adherend surfaces.

Although B-72 was designed by Rohm and Haas primarily as a surface coating and vehicle for flexographic inks, it has been used extensively in con- servation as a consolidant, surface coating, and more recently as an adhesive for glass [2, 3]. The advantages that it presents over the polyvinyl acetate resins include strength and hardness without brittleness, and a higher glass transition temperature (B-72 has a Tg of 40?C, PVA AYAT 28?C). Because of its higher Tg it has less of a tendency to cold flow. B-72 is not as hard (Tukon hardness 10-11) or as brittle as many of the adhesives previously used on archaeological ceramics (e.g. shellac, animal glue, cellulose nitrate), and it will tolerate stress and strain on a join better than the harder, more rigid and inflexible adhesives. The ques- tion of adhesive strength requirements will vary from object to object, and the resulting bond-strength will

Studies in Conservation 31 (1986) 7-14 7

Stephen P. Koob

be affected by a variety of factors [4]. Too often an adhesive is chosen which is too strong for the task at hand and damage to the object results when the join fails and the adhesive pulls away the surface of the object (Figure 1).

Paraloid B-72 demonstrates a moderate hardness that is suitable for application on a variety of materi- als. There is a direct relationship between the mechan- ical properties of bonding, tensile strength, resistance to tear and abrasion, and the molecular weight or degree of polymerization of a linear polymer [5], and B-72 provides excellent mechanical properties and hardness without the brittleness and other disadvan- tages of higher molecular weight resins [1, 2]. With proper preparation and application it provides more than adequate strength for general purpose adhesive applications (Figures 2, 3).

LI

Figure 2 Glass slides joined end-to-end with B-72, supporting 295g weight.

3 Preparation of B-72 as an adhesive

In order to produce an adhesive with excellent work- ing properties certain requirements must be fulfilled. The choice of solvent(s), amount of solids content, use of additives and method of application are all important factors to be considered in the preparation

Figure 3 Pennies joined by the edge with B-72, supporting 295g weight.

of an adhesive. The acrylic resins are known to have slow solvent-release, and the proper choice of solvent and solids content are necessary to achieve a suitable workability. In addition, these factors influence the wettability of the adhesive, its tack or 'open time', and setting time. If the evaporation of the solvent is too fast or the solids content too high, the adhesive will not have a long enough open time or bonding range in which to develop tack and form a strong and con- tinuous film. Too slow an evaporation rate will result in too long an open time, and although the wettability will be improved, tack will be reduced and the adhe- sive will have an unnecessarily long setting-time. Too low a solids content may result in adhesive starvation in the bond-line causing undue stress on the adherend and a poor bond.

3.1 Choice of solvent(s) Experimentation using Paraloid B-72 and various sol- vents and combinations of solvents proved acetone, by itself, to be the most suitable solvent. Acetone provides the fast solvent-release needed for the suc- cessful application of an acrylic adhesive, and is also the least toxic among the commonly used solvents.

Studies in Conservation 31 (1986) 7-14 8

The use of Paraloid B-72 as an adhesive

Slower evaporating solvents such as toluene, xylene or mixtures including acetone and diacetone alcohol were rejected because of the resulting very slow solvent-release and extremely long setting-times. Toluene and slower evaporating solvents are also retained by B-72 for very long periods; thick films on glass slides dried at room temperature remained soft for 3-4 weeks. Moreover, the toxicities of toluene, xylene and diacetone alcohol make them unsuitable for regular use.

Ethanol is compatible with Paraloid B-72 [2], and may be added to form a slower-setting adhesive. Mix- tures containing up to 40% ethanol are usable and are advantageous for the use of B-72 in hot climates (e.g. in the field). Solutions containing over 40% ethanol were found to have poorer tack and too long a setting time.

3.2 Additives Paraloid B-72 does not require the additon of plas- ticizers or stabilizers to modify its mechanical proper- ties and naturally provides suitable adhesive, cohesive and tensile strengths. Fumed colloidal silica (Cab-o-sil or Santocel) can be added to improve the rheological

Figure 4 Paraloid B-72 suspended in a gauze bag.

Studies in Conservation 31 (1986) 7-14

Figure 5 Pouring the adhesive preparation into plain alumi- num tubes.

properties of the adhesive, but is only recommended in very small amounts (0-1% by weight). Larger quan- tities of fumed silica were found to provide little or no improvement in workability, and the preparation of thixotropic mixtures as suggested by Byre [6] resulted in very poor and brittle adhesive bonds.

In addition to controlling the flow of the adhesive, a small amount of fumed silica will better distribute any stress or strain incurred during the solvent evapo- ration and setting of the adhesive film.

3.3 Solids content A solids content of 1:1 by weight (B-72:acetone) was found to provide optimum workability and resulted in an adhesive with excellent tack and a quick setting- time. This equates approximately to an 87-5% solu- tion (w/v), which is considerably higher than the pre- vious suggestions for acrylics [6, 7], or for adhesives based on polyvinyl acetate or cellulose nitrate [8, 9]. This ratio still provides a free-flowing adhesive because of B-72's very low viscosity in acetone. It also reduces the need to introduce a large amount of adhe- sive into the join and therefore lessens the stress which

9

Stephen P. Koob

holds approximately 20g of adhesive and the larger tube, 30g.

K.., .1 ^8,. .. .

...... ..... ...

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Figure 6 Plain aluminum tubes, with nasal tips and solvent- proof caps.

will be caused by loss of solvent and shrinkage during setting.

The proportions should not be altered if ethanol is added since acetone and ethanol have almost identical densities [10].

3.4 Preparation procedure 1:1 Paraloid B-72:acetone (with 0 1% fumed silica) Since it is difficult to dissolve such a high percentage of resin directly into solvent, it is suggested that twice the amount of acetone is used to start with and the solution is then evaporated down to 1:1 by weight.

Weigh out 100g of acetone in a solvent-proof screw- top beaker or jar and stir in 0 g of fumed colloidal silica (approximately one level teaspoon). Add 50g of Paraloid B-72 suspended in a cotton or gauze 'bag' (Figure 4), and close the lid tightly. Once the resin has completely dissolved (1-2 hours at room temperature, if the solution is occasionally agitated), the lid is removed and the container with solution weighed. The container is then left without the lid in a fume cupboard until 50g of acetone have evaporated and a 1:1 proportion of resin:solvent is obtained. The adhe- sive preparation is now ready to be poured into tubes (see Section 4.1 and Figure 5). Larger quantities may be produced at one time; the above directions will produce 100g of adhesive. The small tube in Figure 6

Figure 7 Samples before testing.

3.5 Strength experiments using Paraloid B-72 A simple tensile test was set up using glass slides and the following materials as adhesives (Figure 7):

Paraloid B-72 (1:1 in acetone with 0-1% Cab-o-sil) PVA AYAF (40% in acetone) PVA AYAF (40% in acetone with 0-1% Cab-o-sil) Duco Cement (cellulose nitrate)

The slides were stuck end-to-end and mounted verti- cally so that weights could be suspended from the bottom of the sides (see Figure 2). Six sets of slides were made for each adhesive, three to be tested after 24 hours, and three after 72 hours. The results are listed in Table 2.

Paraloid B-72 demonstrated the strongest bonds and best tensile strength of the adhesives tested. The results using PVA AYAF with Cab-o-sil were similar to B-72 but there was a noticeable difference using PVA AYAF without Cab-o-sil.

The results using Duco Cement were very poor. This adhesive had a very quick setting time but after 24 hours did not show much strength; after 72 hours the joins fell apart during handling. The bond strength increased dramatically in the sample sets which were allowed to dry for 72 hours. All the bond failures were cohesive; no damage was caused to the glass.

Table 2 Strength evaluation experiments (weights are in grams)

Adhesive Set no. 1 Set no. 2 Set no. 3 Set no. 4 Set no. 5 Set no. 6 24 hrs 72 hrs 24 hrs 72 hrs 24 hrs 72 hrs

Duco Cement 0 0 0 0 0 0 PVA AYAF 145 1405 0 1110 295 1550 PVA AYAF (Cab-o-sil) 295 1550 295 1550 295 1700 B-72 610 1550 295 1405 295 2875

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Studies in Conservation 31 (1986) 7-14 10

The use of Paraloid B-72 as an adhesive

4 Application of Paraloid B-72

The method of application can affect the bonding efficiency almost as much as the type and preparation of adhesive. The application of Paraloid B-72 from a collapsible tube solves many of the problems generally encountered with the use of acrylic resin solutions applied by brush or on a cocktail stick (dipped into solution from a jar). The adhesive may be prepared with a higher solids/solvent ratio (Section 3.4) which provides for better workability, less shrinkage, and consequently less stress in the adhesive bond. The solvent supply does not have to be replenished as long as the tube is kept closed between uses, and the adhe- sive can be applied easier, faster, and more effectively. The adhesive is also better controlled, less stringy and more evenly applied, which results in a stronger and more uniform bond. Finally, there is less of a mess, and the conservator can concentrate more on the work at hand than on the cleanup afterwards.

4.1 Tubes Plain aluminum tubes are readily available in a variety of sizes and with narrow nasal tips and solvent-proof caps (Figure 6). Although tubes with larger openings are available, the nasal tips offer better control and application of the adhesive.

The tubes are easy to fill and- close, are collapsible, disposable, and inexpensive. They should be filled to a maximum of two-thirds (Figure 5), to allow for the closing of the end. The end is simply squeezed together, flattened, and folded over tightly three or four times. The end may be crimped using a pair of pliers (Figure 8) to ensure a good seal and to prevent solvent loss or adhesive leakage.

4.2 Priming the substrate Any introduction to the principles of adhesion almost always starts with a discussion of priming or sealing the substrate. Priming the substrate achieves several purposes [11], most important of which are

Figure 8 Filled tubes, with crimped ends.

Studies in Conservation 31 (1986) 7-14

improvements in adhesion and the strengthening of porous substrates. It also reduces the amount of adhe- sive required to form a strong and effective bond. Secondly, priming makes the substrate or adherend more compatible with the adhesive by interacting between the substrate and the adhesive. This results in improved adhesion and the formation of a stronger and more uniform bond.

In addition to the improvements in application and adhesion, priming strengthens and protects the adher- end surfaces as well as allowing any stress or strain on an object to be more evenly distributed.

Priming is of particular importance when the mate- rials to be joined are very porous and the adhesive is solvent-based (commercial adhesives likewise suggest priming or the application of a first coat on porous substrates [12]). Most archaeological ceramics fall into this category and an assessment of the strength and structural body of the ceramic should always be undertaken before any attempt is made to assemble any fragments. Failure to ensure that the substrate is sealed may result in a weaker or unequal bond being formed, and possible subsequent damage to an object.

Paraloid B-72 is ideal for priming, particularly when it is also to be used as the adhesive. It is used in a 5-10% solution in acetone and applied by brush to the edges of the fragments to be joined. Several coats may be necessary for very porous substrates, but one application should be sufficient for substrates with a low porosity.

Non-porous substrates do not require priming because these materials are naturally 'sealed' and do not cause premature loss of solvent during the appli- cation of the adhesive. Some examples of materials in this category are china, porcelain, glass, metals, and non-porous stone (dense marble, flint, obsidian). In general, these materials are strong and do not require the strengthening or protection of a priming coat. Broken fragments may be joined directly.

Priming is not a substitute for consolidation, and friable or flaking substrates will require further atten- tion (Section 4.4).

4.3 Application of Paraloid B-72 on ceramics Fragments to be joined should be clean, free of dirt and grease, primed and dry. The edges of the frag- ments should not be pre-wetted with solvent as this may result in a weak or ineffective join as a result of too much adhesive being squeezed out when pressure is applied.

The adhesive is applied in a thin, uniform line along the center of one of the edges of the pieces to be joined and the pieces are brought together. Immediately after the fragments are mated, they are quickly pulled apart, to check that sufficient adhesive has been applied and has evenly and completely wetted both surfaces. This is only a brief period, of two-three

11

Stephen P. Koob

seconds, but it also allows the solvent to begin evapo- rating from the adhesive. This initial evaporation of the solvent is essential to obtain maximum tack and to prevent too much adhesive from being squeezed out of the join. Too little adhesive is as detrimental as too much. If and where necessary, more adhesive should be added, after which the fragments are rejoined and correctly positioned. Even pressure is now applied to the fragments to ensure a close bond and to squeeze out surplus adhesive. Because of B-72's excellent tack, the fragments need only be held for 10-20 seconds (longer for larger pieces), at which point they can be set down, balanced so that the weight of one fragment (usually the smaller) is evenly distributed over the bottom fragment. The joined fragments are now propped in this balanced position, against an immov- able object, or in a dish-rack or sand-tray. Tension tape is often useful to hold large fragments or compli- cated joins in position.

After one-two minutes, the excess adhesive can be cleaned off using a cotton swab or soft brush wetted with acetone, or left until the bond has completely set. The advantages of cleaning before the B-72 has set hard are that the cleanup requires less solvent and time, and the join may also be examined for accuracy, preferably under a binocular microscope.

If the fragments have not set properly, they may be

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Figure 9 Large black-figure amphora (57cm high), restored using Paraloid B-72 as the adhesive.

easily realigned at this point by the judicious applica- tion of more acetone (by brush) along the join. Too little solvent will not soften the bond, and too much solvent will loosen the join completely. Patience and experience are the best guides. After the bond has set hard it may require packing with cotton wool soaked with solvent, or complete immersion in solvent to loosen it. A good join will not come apart easily (Figure 9).

4.3.1 Thermoplasticity An alternative to the use of solvent to adjust a join is to take advantage of B-72's thermoplasticity and apply gentle heat to the join. After a few minutes under a desk lamp or hair dryer, the resin softens by being heated above its Tg, and the fragments may be realigned and held in position until the resin has cooled and reset. This is particularly useful where an excess of adhesive has been intentionally introduced into a join because the fragments have been damaged by previous sanding or scoring of the edges. In these cases realignment is often necessary because the edges do not fit tightly and the application of solvent would soften the join too much. This property may only be used if the object being repaired can withstand gentle heat.

4.3.2 Smallflakes When it is necessary to attach small flakes, chips, or slivers of glaze, a microscope should be used along with the following procedure.

A small drop of adhesive is placed on the join sur- face and the adhesive is then thinned by touching the area with a brush wetted with acetone. The flake is then carefully positioned and lightly pressed into its final position. In this manner a good bond is obtained with no excess adhesive in the join. Care should be taken not to apply too much solvent or the adhesive will be completely dissolved out of the join.

4.3.3 Stress cracks Stress cracks in ceramics can be strengthened or joined (if the fragments are not too far apart) by dripping or injecting the adhesive, suitably thinned, with a syringe into the crack. After waiting a few minutes to permit initial evaporation of the solvent, pressure is applied across the join by means of tension tape or the use of an elastic band (if the object is whole) of suitable size and strength. The adhesive should be left to dry completely, preferably 24 hours for large cracks, before the tape or elastic band is removed.

4.4 Friable or weak ceramics As mentioned in Section 4.2, a detailed examination of the strength of the ceramic should be undertaken before any fragments are assembled. Friable ceramics

Studies in Conservation 31 (1986) 7-14

m

12

The use of Paraloid B-72 as an adhesive

and soft terracottas may require complete consoli- dation before any joining can safely be undertaken. With these materials it is often preferable to consoli- date the entire fragments rather than sealing or prim- ing the edges. Priming will improve the adhesive bond but stress or strain on the join may later result in damage. Although the bond itself may not separate, the weaker unconsolidated ceramic will fracture at the interface of the consolidated and unconsolidated areas. It should be remembered that the strength of any adhesive bond is only as strong as its weakest member [13]. Paraloid B-72 is recommended as the consolidant for weak and friable ceramics, applied in toluene or acetone. The fragments should be com- pletely dry before any assembly is undertaken.

4.5 Non-porous ceramics Non-porous ceramics require special handling once the fragments have been joined together using B-72. It will be necessary to tape or hold fragments in position for a much longer period than is necessary with rougher porous materials. The two factors which need to be considered are the solvent escape from the adhe- sive and the smaller surface area to which the adhesive is bonding. Glassy materials such as china and por- celain, by their very nature, have relatively smooth edges and less surface area when compared to the broken edges of an earthenware vessel. In all instances solvent will evaporate from every available surface, but it is noticeably slower from a dense, non-porous join. In porous ceramics it is advantageous that prim- ing or sealing the substrate retards the evaporation rate but the opposite is desirable for non-porous materials. With non-porous ceramics the solvent is unable to excape from within the substrate and will escape primarily along both sides of the adhesive line. The solvent evaporation rate and setting time of the adhesive will vary considerably from object to object and are governed by the ambient conditions, thickness of the join, and properties of the materials being joined. Assembled fragments should not be handled until the adhesive has set completely. Very thin china or porcelain may be handled in 5-10 minutes; very thick fragments in two-three hours. Figure 10 shows a china plate which was joined using B-72. The adhe- sive had set sufficiently in one hour for the plate to be laid flat; the plate could not be pulled apart (by two people) after 24 hours. Adhesive tests (Table 2 and Section 3.5) using glass slides showed that B-72 was stronger than either PVA AYAF or Duco Cement (cellulose nitrate).

The reopening of a joint, as mentioned in Section 4.3, is effective in controlling the initial solvent evapo- ration of the adhesive, and can be used to most advan- tage when adhering non-porous ceramics. The frag- ments should be kept apart as long as possible, but not beyond the open time or effective bonding range of the

Studies in Conservation 31 (1986) 7-14

adhesive. Otherwise too much solvent will have evap- orated and the adhesive will not have enough tack to bond effectively.

fd "rt~\.'

-

..........

Figure 10 China plate, previously joined with cellulose nitrate (top) and joined using B-72 (bottom).

5 Other archaeological materials

The approach to joining other archaeological materi- als is similar to that of ceramics. Materials in a friable condition will require consolidation before joining, and porous materials such as ivory, bone, porous stone and corroded metals should be primed. Non- porous materials such as metals, stone and glass may be joined directly. For very thin glass or thin metals it may be desirable to assemble the joins first with tape and drip a thinner solution of adhesive along the join, where it will be taken into the join by capillary action. Difficulty may be encountered with the fast solvent evaporation (of acetone) which will increase the vis- cosity of the adhesive and impede penetration. In these circumstances it may be necessary to thin the

13

Stephen P. Koob

adhesive continuously with solvent during application or, alternatively, to choose a slower evaporating sol- vent or solvent mixture.

6 Conclusions

Paraloid B-72 has achieved widespread recognition as a stable and dependable consolidant and has found a place in almost every conservation laboratory. It also makes an excellent adhesive which is strong and tough without being brittle and is suitable for use on a wide variety of materials. The difficulties in workability can easily be overcome by proper preparation and appli- cation and, if used correctly and adjusted as needed, it will satisfy a majority of conservators' general needs.

Suppliers of materials

Paraloid B-72: Rohm and Haas Company, Philadelphia, PA 19105, USA. Cab-o-sil: Cabot Corporation, 125 High Street, Boston, MA 02110, USA. Santocel (silica aerogel): Frank W. Joel Ltd, Oldmedow Road, Hardwick Industrial Estate, King's Lynn, Norfolk PE30 4HH, UK. Plain aluminum tubes: Teledyne Packaging, 4th and Towns- end Streets, P.O. Box 640, Chester, PA 19016, USA. PVA AYAF: Union Carbide Corporation, 270 Park Ave- nue, New York, NY 10017, USA.

References

1 FELLER, R. L., 'Thermoplastic polymers currently in use as protective coatings and potential directions for further research', ICCM Bulletin 10 (1984) 5-18.

2 Acrylic Thermoplastic Acrylic Ester Resins, Rohm and Haas Company, Philadelphia PA, USA (1983).

3 TAYLOR, T. H. JR., 'In situ repair of architectural glass' in Adhesives and Consolidants, IIC, London (1984) 202-204.

4 BRADLEY, S., 'Strength testing of adhesives and consoli- dants for conservation purposes' in Adhesives and Consolidants, IIC, London (1984) 22-24.

5 MARK, H. F., 'Cohesive and adhesive strength of poly- mers, Part 1', Adhesives Age 22 (1979) 35-38.

6 BYRNE, G. S., 'Adhesive formulations manipulated by the addition of fumed colloidal silica' in Adhesives and Consolidants, IIC, London (1984) 78-80.

7 SNOW, C. E., and WEISSER, T. D., 'The examination and treatment of ivory and related materials' in Adhesives and Consolidants, IIC, London (1984) 141-145.

8 MIBACH, E. T. G., 'The restoration of coarse archae- ological ceramics' in Conservation in Archaeology and the Applied Arts, IIC, London (1975) 55-61.

9 DOWMAN, E. A., Conservation in Field Archaeology, Methuen & Co Ltd, London (1970) 71-72.

10 WEAST, R. C., (ed.), CRC Handbook of Chemistry and Physics, CRC Press Inc., Florida, USA, 59th edn (1978-79) C-296, C-461.

11 HOUWINK, R., and SALOMON, G., (eds.), Adhesion and Adhesives, Volume 2, Applications, 2nd edn, Elsevier Publishing Co., London (1967) 9.

12 H. M. G. Heat and Waterproof Adhesive, H. Marcel Guest Ltd, Collyhurst, Manchester 9, England.

13 SKEIST, I., (ed.), Handbook of Adhesives, 2nd edn, Van Nostrand Reinhold Company, New York (1977) 11.

STEPHEN P. KOOB, born 1951, MA in Classical Archaeology, 1976, Indiana University, Bloomington IN, USA; BSc in Archaeological Conservation, 1980, Institute of Archae- ology, University of London. Conservator of the Agora Excavations and Collections, American School of Classical Studies, Athens, Greece, since 1980. Currently employed as conservator at the Freer Gallery of Art. Author's address: Freer Gallery of Art, Smithsonian Institution, Washington, DC 20560, USA.

Resum---La preparation et l'application appropri6e du Paraloid B-72 en fait un excellent adh6sif pour les ceramiques archeologiques et les autres materiaux. On montre qu'il est indispensable de comprendre les principes de l'adh6sion pour un usage satisfaisant des adh6sifs en solution.

Auszug-Die ordnungsgemlBe Zubereitung und Aufbringung von Paraloid B-72 machen es zu einem aus- gezeichneten Klebstoff fur archiologische Keramiken und andere Materialien. Ein Verstandnis der Prinzipien der Adhasion ist fur die erfolgreiche Aufbringung von Losungsmittelklebern wesentlich.

Studies in Conservation 31 (1986) 7-14 14