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Acid preparation of fossils using sulfamic
acid, a weak organic acid, and its advantages over acetic and formic acid preparation
Carlos B. Padilla & Mary Luz Parra
Fundación
Colombiana
de Geobiología
Fundacion
Colombiana
de Geobiologia
Large Volume of Calcareous Matrix : we pursued less immersions
• Authors of Vertebrate Paleontological Techniques vol 1 encompass
acid preparation with
formic and acetic acids and suggest that discussions with Daniel
Gouget
(Institut
de
Paleontologie
du Museum, Paris) supported their use of formic acid.
• They felt the stronger formic acid was more stressful to the fossil material but would require
many less immersions than necessary with acetic acid.
Vertebrate Paleontological Techniques vol.1, Cambridge University Press, Patrick Leiggi and Peter May , 1994
Sulfamic
Acid (H2
NSO3
H)
• Also known as amidosulfonic
acid; amidosulfuric
acid, sulphamic
acid;
aminosulfonic
acid; kyselina
aminosulfonova; suphamidic
acid; sulfamidsäure
in
German; acido
sulfamidico
in Spanish; acide
sulfamidique
in French, is a weak
organic acid with marked characteristics that set it apart from acetic and formic
acids:
• It is a stronger weak acid than both acetic and formic.
• Solid, crystalline powder which dissolves easily in water.
• A powder with melting point of 205°C.
• Non hydroscopic.
• Very stable and easy to transport.
• Less toxic
• Good history of use, common in domestic and industrial cleaning products
designed to remove scale deposits.
Logarithmic Dissociation Constants (pKa) at 25°C and NFPA Hazard Ratings
NFPA
Rating
State fumes pKa health Fire reactivity
Sulfamic
Acid
solid no 1.18 2 0 0
Formic
Acid
liquid yes 3.74 3 2 0
Acetic
Acid
liquid yes 4.76 2 2 2
Commercial Sulfamic
Acid with pH indicator
The Procedure
• Follows most traditional guidelines.
• Time frames and concentrations varied.
• Initially used all three acids 5% by weight by volume, eventually reduced to 4% for rapid matrix removal
where significant fossil is not exposed.
• Once significant fossil material is exposed, acid reduced to 2% weight by volume for most work providing balance between time, number of
immersions and bone integrity.
Comparative TestingAcid bath : 100 ml 2% (wbv)
Sample Matrix size: 10 gram fragment
Cycle time: 2hrs.Sample CBP‐17 CBP‐4 CBP‐21
Formic
Acid:
Cycles 4 4 7
Start
pH 2 2 2
End
pH 3 4 2
Residual matrix 0 gms 0 gms 7 gms
Acetic
Acid
Cycles 7 6 7
Start
pH 2 2 2
End
pH 4 3 2
Residual matrix 0 gms 0 gms 7 gms
Sulfamic
Acid
Cycles 4 4 7
Start
pH 1 1 1
End
pH 1 1 1
Residual matrix 0 gms 0 gms 6 gms
Protection with Paraloid B-72
Preliminary cleaning
NO OK
CONTROL(porosity, etc)
Acid Inmersion
Neutralization
Mechanical preparation of soft parts
SUFAMIC ACID ACID(WASH
AND DRY)PARALOID B-72 inALCOHOL
SULFAMIC ACID(4-2%)
Ready More prep.needed
(RUNNING WATERAND DRY )
WASH
Pliosaur
Specimen FCG‐CBP/004
Chose the segments and tested
Control of acid activity in fractures
Repeat same procedure with more segments
12/16/02 Right lateral 01/09/03 Left lateral
01/14/03 Left lateral 01/30/03 Left lateral
Ventral and Dorsal Views
Sutures and foramina well defined, excess B-72 removed
Lateral right and left sides FCG‐CBP/004
Delicate sclerotic rings
Jan. 1999 Plesiosaur Specimen FCG‐CBP/003
CT Scan as a tool
to
preview
fossil material while
acid
cleaning
Again well defined sutures and foramina
Ventral view
Vertebrae also enclosed in calcareous matrix
Vertebrae ventral and lateral
Articulated cranium
Findings
• When all three acids are used for the same period of time per
cycle, formic and sulfamic
will remove the same amount of
matrix by weight, acetic at half the rate. This applies until the
initial pH changes.
• Whereas the pH changes with formic and acetic acids after 2
hrs of work, sulfamic
maintains the original pH up to 12 hrs
later allowing for longer cycles without changing the acid
bath.
Mechanical and Acid vs
Acid preparation
FCG‐CBP/3
Mechanical and Acid preparation
• Cycle time:
3‐5 hrs
• (7) seven cycles with 4%
acid.
• (3) three cycles with 2%
acid.
FCG‐CBP/4
Only acid preparation
• Cycle time: 3‐5 hrs
• (15) fifteen cycles with 4%
acid.
• (6) six cycles with 2% acid.
Matrix thin sections and residue analysis
FCG-CBP-21
FCG-CBP-17
FCG-CBP-4
Grainstone (Durham 62)Haematite 8%Micro sparite 87%nummulites
Grainstone (Durham 62)Haematite 7%Micro sparite 86%
Gypsum 47%Haematite 47%
Clay 13%Quartz 4%Opaques 83%
Clay 88%Quartz 5%Opaques 2%
Clay 88%Quartz 2%Opaques 9%
Conclusions
Many Thanks to:• Mary Luz Parra, Fundacion
Colombiana
de Geobiologia.
• Jane Mason, Senior Museum Preparator, University of California Museum of Paleontology.
• Mark Norell, Chairman and Curator Div. of Paleontology, American Museum of Natural
History.
• Amy Rachel Davidson, Senior Principal Preparator, Dept. of Paleontology, American Museum
of Natural History.
• Leslie Noè, Curator of Natural Science, Thinktank, Birmingham Science Museum.
• Carlos Jaramillo, Smithsonian Tropical Research Institute, Panama.
• Maria Paramo, Research Professor, Universidad Nacional
de Colombia.
• Eugene S. Gaffney, Curator, Dept. of Paleontology, American Museum of Natural History.
• John Maisey, Curator and Axelrod Research Chair, American Museum of Natural
History.
• Fernando Etayo, Researcher, INGEOMINAS.
• Diego Pol, M.E.F., Trelew, Patagonia Argentina.
• Marcela Gomez, CASP, University of Cambridge.
• Tatiana Gaona, INGEOMINAS ( Instituto
Colombiano
de Geologia
y Minas).
• Juan de Dios Parra, Fundacion
Colombiana
de Geobiologia.
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