Darren Tanke’s Gorgosaurus preparation 5: fixing the cracks

The report covers November 3-4. More of the Gorgosaurus skull was uncovered, but the work slows down a bit on account of shattered rock, cracks in rock, and complex anatomy. Some of the gorgosaur bones were hollow in life or quite thin (playing card thickness) so work has to go more slowly. Additionally some of the teeth are being detailed and the chin region restored.

Cracked fossil bone needs repair. Traditionally cracks were simply filled with plaster but this is only a filler, it has little to no bonding strength and can get onto the adjacent good bone surface obscuring critical details to researchers. Another way to fix cracks is to inject glue until the crack fills up, but I have seen instances where the crack was bottomless and the glue was dripping out of the bottom of the field jacket. No good! This means the specimen is now effectively glued to the jacket which is something very hard to impossible to reverse. More control was clearly needed.

Over a decade ago I developed a technique whereby tissue paper (brown in color and unbleached or colored) is put into the cracks. Small pieces are pulled off the sheet of tissue and loosely rolled between thumb and forefinger. This “sausage” of paper is then laid atop the crack and pushed in with a sharp scalpel blade which chops up the fibres and pushes the tissue paper down. This process is repeated (if necessary) until the crack is filled to near the top. Then strong and runny glue is carefully squirted onto the paper. The paper soaks up the glue so it does not drip through to the jacket. Several coats of glue will make the glued paper progressively darker, but once dry it is still easily differentiated from the real bone by color and texture. The use of unbleached and uncoloured paper is made because of no added chemicals that might react over time. Specimens so prepared 15 years ago are still in excellent shape. I show a sequence of events to repair a crack in the left postorbital bone. The final work on this and other cracks will be done when the last preparation of the skull and skeleton is done. This paper technique is also good for filling cracks in matrix- the same procedure is done but then ground up matrix is sprinkled on top of the wet glue. When dry and the loose matrix dust are brushed away, the crack not only disappears, but is now firmly stabilized.

The Gorgosaurus skull picture shows it after 5 days of preparation work on November 4th. I can only put a half day on the Gorgosaurus on Nov. 5th so the next progress report will not be submitted until early next week.

More to come soon! All photos here and in the series are owned by Darren Tanke and the Royal Tyrrell Museum.

7 Responses to “Darren Tanke’s Gorgosaurus preparation 5: fixing the cracks”

  1. 1 Mark Robinson 08/11/2010 at 2:27 am

    Fantastic stuff, Darren. I really appreciate that you take the time to explain the process in detail. I also like that you think to include little things such as some of Gorgy’s bones being as thin as a playing card – that’s not usually obvious to a layperson and is rarely stated in the literature.

    • 2 Darren Tanke 08/11/2010 at 7:28 pm

      Glad everyone is finding this blog interesting. It is a fun specimen to prepare and having found it myself it is “mine” and therefore all the more special for me to work on. Some researchers are already wanting to study it!

      • 3 David Hone 08/11/2010 at 7:39 pm

        Were it not for the fact that there are obvious people at the Tyrell and in Canada and North America in general, I’d have asked myself!

  2. 4 intercostal 08/11/2010 at 2:29 pm

    I am really liking this preparation series; it’s very interesting to see it step-by-step.

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