Darren Tanke’s Gorgosaurus preparation 18: that superb skull

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.

10 Responses to “Darren Tanke’s Gorgosaurus preparation 18: that superb skull”

  1. 1 David Stern 29/01/2011 at 8:54 pm

    I’m wondering when it would be possible if ever to not have to physically apply latex to get a mold of a bone. In other words using computers and a laser to measure the entire surface in enough detail to make exact models of it?

    • 2 Darren Tanke 29/01/2011 at 9:06 pm

      That is a great question. I am sure the technology exists, but am certain we have not explored it at our museum. I suspect it would be very expensive to acquire the machinery and software. Many of the field and laboratory techniques we use have not changed much in over 150 years and still work for us now so we continue to use “old style” techniques. That is not to say we don’t embrace new technologies, such as power tools, vehicles, helicopters, glues, plasters, casting plastics, fibreglass resins, etc. Some of these too are pricey (ie. helicopters), but are thus carefully considered. For example, what is more expensive- 5 people dragging a heavy block for 1 week through the badlands (and damaging themselves and the environment, as well as jarring the rare fossil inside) or hiring a helicopter to do the same job in 5 minutes? Our casting programme is pretty small and adopting new technologies such as you suggest would be out of our price range. Come to think of it, I cannot offhand think of anyone in the professional paleo community regularly using lasers and scanners and then making casts from the data. All do molding and casting the old way.

      • 3 Mike Taylor 01/02/2011 at 2:46 pm

        This is how RCI made the “cast” of the Giraffatitan brancai skull HMN T1 to go on the remounted skeleton of the paralectotype HMN SII: they laser-scanned the real skull, and printed off the cast. (In fact, because of the digital approach, they were able to be a bit cleverer than that, and scaled the cast skull slightly, to make it a better match for the rest of the skeleton. Impressive stuff.)

        That said, I don’t know how precise the process is. It’s certainly good enough for a gallery exhibit — they made a spare skull which sits at ground-level in the Berlin exhibit, and it looks just fine — but I didn’t look at it closely enough to see whether it would be good for scientific work.

      • 4 Darren Tanke 09/02/2011 at 5:11 am

        Thanks Mike, I did not know that. I think RCI has a huge molding and casting budget compared to ours. Maybe I’ll contact them and see how much it costs.

    • 5 David Hone 30/01/2011 at 12:30 am

      I have actually experimented with this but (stupidly and sadly) never wrote it up. We scanned the skull of Fodonyx (now Bentonyx) with a 3-D laser and created a rapid prototyped model. It was OK with about 0.5mm resolution. We were experimenting with repairing breaks and restroing missing parts digitally as well such that a further printed model would be ‘better’ than the original. You can see the prototyped models here: http://www.descam.de/anwenderberichte_palaeontologie.htm

  2. 6 BJN 31/01/2011 at 5:49 pm

    Beautiful. Thanks for sharing the preparation with us.

  3. 7 G. I. Deneva 05/02/2011 at 11:36 am

    Hey, i’d like to publish a very shortened version of the series (when it is finished). I need a permission to use some of the pictures. Would you please help me with that?

  1. 1 Darren Tanke’s Gorgosaurus preparation: final roundup « Dave Hone's Archosaur Musings Trackback on 22/02/2011 at 9:00 am
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