Using the methyl cellulose poultice method to remove plaster and burlap - A case study on Triceratops bone

The dinosaur collection at the Natural History Museum, London (NHM) includes a Triceratops skull (NHMUK PV R 3886), purchased from Charles Sternberg in 1909. While most of the skull is on public display in the Dinosaurs gallery, two large sections of the frill (the squamosal bones) had been replicated for the display and the originals left in storage. With much of the fossil bone obscured by plaster of Paris, the original frill sections were deemed of limited use to science in their current form. A work request was received to strip away as much artificial material as possible to determine the extent of the original fossil material. An air scribe fitted with a chisel stylus proved initially effective, but soon revealed an additional obstacle – layers of hessian underneath. The methyl cellulose poultice method was used to swell the hessian, aiding softening of the plaster, and allowing layers to be torn off in strips. The fine layer of plaster remaining on the bone was removed, where possible, with a Split-V ultrasonic tool. This sequence of treatments can be utilised at minimal risk to specimens in similar situations when a hessian and plaster jacket has been applied but a separator layer has been omitted.