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 (H 2 NSO 3 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 StatefumespKahealthFirereactivity Sulfamic Acid solidno Formic Acid liquidyes Acetic Acid liquidyes

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 Testing Acid bath : 100 ml 2% (wbv) Sample Matrix size: 10 gram fragment Cycle time: 2hrs. SampleCBP-17CBP-4CBP-21 Formic Acid: Cycles447 Start pH222 End pH342 Residual matrix0 gms 7 gms Acetic Acid Cycles767 Start pH222 End pH432 Residual matrix0 gms 7 gms Sulfamic Acid Cycles447 Start pH111 End pH111 Residual matrix0 gms 6 gms

Protection with Paraloid B-72 Preliminary cleaning NOOK CONTROL (porosity, etc) Acid Inmersion Neutralization Mechanical preparation of soft parts SUFAMIC ACID ACID (WASH AND DRY) PARALOID B-72 in ALCOHOL SULFAMIC ACID (4-2%) Ready More prep. needed (RUNNING WATER AND 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 lateral01/09/03 Left lateral 01/14/03 Left lateral01/30/03 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 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.