An Initial Investigation into the Acquisition and Conservation
History of the Fossil Marine Reptile Stenopterygius acutirostris
(Owen) from the Upper Liassic near Whitby, Yorkshire, England
Sandra D. Chapman & Adrian M. Doyle
CONSERVATION
Making a cast
Prior
to any preparation it was decided to make a cast of the specimen
areas that were due to be investigated for record keeping and for
part of the research. Silicone rubber is a preferred medium for
mould-making and skin moulds were produced by applying three layers
of rubber which were backed with Jesmonite® reinforced with
glass fibre tubing. Plaster of Paris was chosen to make the cast due
to its cheapness and the need to cut the cast up into individual
sections to attempt rearrange the individual elements of the paddle.
Moulds and casts were taken of the main paddle, the end of the
broken snout and the end of the right paddle.
Conservation history
The Palaeontology Conservation Unit has extensive treatment records for the last 40 years and these revealed that the specimen was subject to previous laboratory work in 1983.
The treatment record states:
- The specimen was cleaned with solvents and consolidated with a synthetic resin - alvar (polyvinyl acetal) which is no longer used today.
- Cracked and loose plaster was mechanically removed and replaced with plaster, scrim and wood.
- Loose plaster and rock fragments were removed from underneath the main body.
- The 'tail section' was dismantled and reassembled with a synthetic filler AJK Dough (Alvar Jute Kaolin Dough - no longer used). Additionally, an annotated pencil diagram was used for component relocation.
- The 'snout' area had a recess for where the former bone rested. This had been levelled with Plaster of Paris.
- Repaired areas were painted out.
Removal of the matrix and surrounding plaster
A decision was made to concentrate on two parts of the specimen that would hopefully help us identify areas of reconstruction. In order to minimise the disturbance to the whole specimen, it was decided to use an electrically driven flexible drive with a rotary diamond-cutting disk to cut through the matrix. Once areas had been cut, large areas of matrix were removed with hammer and chisel. For more delicate work, a pneumatic percussion air-pen (a commonly used preparation tool) was used when close to the specimen surface. This entire procedure required the use of a vacuum cleaner for dust extraction and for the operator, safety spectacles and a dust mask. The removed plaster and matrix was carefully bagged and recorded for further investigation.
