The Gorgosaurus skull (left side) was finished on January 27th. A very close visual inspection was made over the entire skull and any remaining bits of bone-colored glue, rock or sand grains removed with a scalpel carrying a #15 blade which I reshaped to suit my requirements on an oilstone and resharpened every 10 minutes or so. A finger was then run over the the entire specimen. Any bumps, pointy bits, or rough patches were reinvestigated to comfirm they were actually bone. If not they were removed. Then a magnet was passed over the entire specimen and surrounding matrix. Magnets are not in a standard preparators toolbox but I use one at the end of each project. Several types of small wire brushes were used to carefully clean the bone surface over the past months and they do shed bristles, some quite tiny (2 mm). This specimen is to be CT-scanned by researchers in the next few months. I don’t want them coming back to me saying some foreign metal object compromised their CT-scan results. While I have kept the Gorgosaurus skull clean by brushing and careful vacuuming, I was still able to get about half a dozen metal brush bristles with the magnet.
I then washed the skull with tapwater and a standard toothbrush with firm bristles. The brush was made wet, then vigorously shaken out so it was only damp, not dripping wet. The bone surface was carefully scrubbed in a circular motion. The brush was then rinsed out in a clear container of tapwater. Each time the brush was rinsed this way, it was easy to see the water becoming more and more dirty as more of the clay particles and other minerals were removed from the bone surface. When the brush rinsed clean after each scrub it was time to stop. Then the skull was put under a desklamp with a floodlight bulb to warm up and evaporate any remaining water. The skull was then allowed to sit for an hour and cool down. This is important for the next step. A heated specimen, having more glue added to it, can have the acetone solvent “boil”, ruining the effect one is now trying to achieve.
A thin mnix of Acryloid glue and acetone was mixed and a thin layer brushed over the specimen and “scrubbed” into the bone with tight circular motions so it soaked in deeply. This glue seals any microcracks and holes. This is vitally important as the specimen is to be latex molded soon. Latex, being brushed on, gets into every nook and cranny. It can be pushed through a crack where it can expand a bit. When the cured latex is removed, the expanded bits of latex “grab” onto or anchor into the bone and require more force to pull out. This pulling action can damage the area involved and compromise the safety of the entire specimen. So it is best to seal over these potential problem areas now, rather than deal with breakage later. However, it is almost always inevitable that some breakage occurs during demolding. Once the entire skull and teeth were so treated and the glue dried within minutes, I was able to step back and get that feeling of a job well done, that every preparator experiences at the end of a project (in this case the skull only)I. I still need to finish off parts of the legs and ribs before molding happens. A molding meeting is happening the middle of next week to discuss how the molding/demolding will proceed. Hopefully in about 2-3 weeks the molding will begin- that process taking about 5 days.
[Dave adds: And now, here it is. The complete and final and finished version of the left side of the skull. Scale bar is 10 cm. And just a couple of months ago it still looked like this].
All photos here and in the series are owned by Darren Tanke and the Royal Tyrrell Museum.