Acid preparation of fossils using sulfamic acid, a weak organic acid, and its advantages over acetic and formic acid preparation

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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

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Fundacion Colombiana de Geobiologia
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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
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Sulfamic Acid (H2NSO3H)

• 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 205C.
• 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.

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Logarithmic Dissociation Constants (pKa) at 25C
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
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Commercial Sulfamic Acid with pH indicator
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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.

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Comparative Testing

• Acid 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
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ACID (WASH AND DRY)
Preliminary cleaning
SUFAMIC ACID
PARALOID B-72 in ALCOHOL
Protection with Paraloid B-72
CONTROL (porosity, etc)
NO
OK
Acid Inmersion
SULFAMIC ACID (4-2)
Neutralization
(RUNNING WATER AND DRY )
WASH
Mechanical preparation of soft parts
Ready
More prep. needed
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Pliosaur Specimen FCG-CBP/004
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Chose the segments and tested
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Control of acid activity in fractures
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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
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Ventral and Dorsal Views
Sutures and foramina well defined, excess B-72
removed
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Lateral right and left sidesFCG-CBP/004
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Delicate sclerotic rings
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Jan. 1999 Plesiosaur Specimen FCG-CBP/003
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CT Scan as a tool to preview fossil material
while acid cleaning
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Again well defined sutures and foramina
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Ventral view
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Vertebrae also enclosed in calcareous matrix
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Vertebrae ventral and lateral
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Articulated cranium
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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.

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Mechanical and Acid vs Acid preparation

• FCG-CBP/3
• Mechanical and Acid preparation

• FCG-CBP/4
• Only acid preparation

• Cycle time 3-5 hrs
• (7) seven cycles with 4 acid.
• (3) three cycles with 2 acid.

• Cycle time 3-5 hrs
• (15) fifteen cycles with 4 acid.
• (6) six cycles with 2 acid.

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Matrix thin sections and residue analysis
Grainstone (Durham 62) Haematite 7 Micro sparite
86
Clay 88 Quartz 5 Opaques 2
FCG-CBP-4
Grainstone (Durham 62) Haematite 8 Micro sparite
87 nummulites
Clay 88 Quartz 2 Opaques 9
FCG-CBP-17
Clay 13 Quartz 4 Opaques 83
Gypsum 47 Haematite 47
FCG-CBP-21
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Conclusions
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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.