Posts Tagged 'preparation'

Darren Tanke’s Gorgosaurus preparation 32: Removing the field jacket 2

Some pieces come off in large sections. A block of wood is useful as a fulcrum with the screwdriver(s) to pry up the plaster bandages. After 1.5 days of pulling and tearing, most of the jacket was off, rock was showing and the ilium uncovered in the field was also seen again for the first time in several years. The skull was outlined again with a red felt pen using the drilled holes. As the jacket got thinner, a quite large piece wanted to lift off the skull area. This was too big, so I used a cast cutter to cut two parallel lines through the jacket and pulled out the plaster and burlap in between.

This separated the remaining jacket into two pieces and the plaster/burlap covering the skull section was lifted off easily. By doing this, the jacketed skull was seen. The rags and black plastic sheeting was exposed and removed- the latter with a razor blade. The skull jacket looks odd with white sandstone and dark brown mud, but the latter was a poultice I mixed up and put on the exposed snout to protect it from the jacket- I did not want the jacket pressed right against the skull.

The poultice of dried mud was removed and preparation on the skull begun again. The skull is definately incomplete on this side and the bone seems more poorly preserved- the bone is very splintery. Several of the teeth show white meandering markings (root etchings) made by modern plants as they grew against the specimen. It is thought the roots leach minerals out of the fossil with possible negative effects on the fossil. The rest of the exposed rock was allowed to dry out and when done, glue was squirted into the cracks, etc to stabilize it for the upcoming preparation.

Fieldwork for me starts very soon so these will likely be the last postings from me for some time. [Actually Darren has already gone I think, I’ve just had this sat waiting for a while].

Darren Tanke’s Gorgosaurus preparation 30: turning the block 2

The block is lifted off the table by a large overhead crane (it runs on tracks mounted near the ceiling and can move 4 directions) and lowered onto a pallet jack. Then it was taken to a larger empty work area nearby. The red lifting straps are readjusted so when the block is lifted it now stands vertically, then the whole crane is moved over and simultaneously the cable lowered so the jacket comes to rest “upside-down”. Actually it is now in its original field orientation. The flipped block is put back on the pallet jack, wheeled over to the work desk, the straps readjusted a final time and the block lifted back onto the table. This work is always done with others helping for safety reasons.

Once the block was on my work table I was able to refind the holes I drilled through days ago and “connect the dots” with a red marker pen. Now I  know exactly where the skull is positioned inside. Now the manual labor of pulling the jacket off begins!

Darren Tanke’s Gorgosaurus preparation 27: burlap additions

All of the exposed bone and rock was then covered up with wet tissue paper. The low spots on the body that were infilled with plaster earlier were in need of a separating layer too – I again used a cut up plastic garbage bag. Then the main support jacket was ready to be made.

A bolt of dry burlap was cut up into various-sized pieces first- enough (and more) for the job that needed to get done next. One always cuts more than needed- you don’t want to run out of cut burlap near the end of a project! The next person doing a plaster/burlap job can always use your cut up pieces. All the cut burlap pieces were put into water and allowed to soak for 15-20 minutes then wrung out. Now we are ready for the plastering phase.

Darren Tanke’s Gorgosaurus preparation 25: completing the skull jacket

The skull was then jacketed. A picture of the skull (without separator) shows the bandaging (jacketing) material used. It is a hospital product of cloth impregnated with dry plaster. It is used there to set and hold broken bones in place, but is also ideally in the lab or field for collecting and stabilizing a fossil specimen. [I have few posts on this on the Musings – here, here and here]. You simply soak it in a pan of water for about 5-10 seconds, squeeze out excess water and then apply it to the item being jacketed. It can be cut into pieces as shown or dispensed right off the roll. About 6 layers were used.

The wooden frame was put back on the jacketed skull and more hospital-type bandages used to attach it. I typed up the specimen number in enlarged font, printed it off, then cut the number out and glued it in place with white glue. It looks messy at first but the glue dries clear, sealing the number inside.

Darren Tanke’s Gorgosaurus preparation 21: The end

The Gorgosaurus preparation on this side is now completed. On February 18th, Dr. Philip J. Currie came to examine the specimen and do some research on it. He will likely return and do more once the specimen is flipped over.

The specimen has now acquired a Dinosaur Provincial Park quarry number: the quarry site is now known as quarry 257. The only thing that needs to be done on the Gorgosaurus block now is the addition of a thicker, penetrating glue into all the rock surrounding the bones so it resists the deep penetration of the curing silicone molding compound and hold together when the mold is removed. This gluing will be done on February 22nd and will then be left for a week or so to fully dry while I am engaged in some other work. This means the rock will now be harder on the other side, but recall the glue is acetone-based so I can just use pure acetone to soften the glue as required. Even though the main block is done (on this side), there are still some small blocks that were removed during the initial fieldwork in 2009. These consisted of two blocks, one an epipterygoid (a palate bone) and a long mid-dorsal rib, with another unidentified bone alongside. The epipterygoid (opened jacked shown above)was started today and went quickly. It will be fully prepared out of the rock. A crew was working near the quarry in 2010 and when they revisited the site, they found another bone being exposed by erosion.

Normally we dig 1 metre past the last bone and stop there. This bone was a little beyond that and it was missed, so was collected in 2010. I worked on that bone as well and see now it is an angular- one of the lower jaw bones positioned at mid-length along the bottom edge. It is good to have these skull bones but they tell us the skull will not be as complete on the other (upper) side as the side (bottom) we have been watching on this blog.

Next updates will cover the molding process. I don’t know when this will start as some other Tyrrell staff do that work and they are (or soon will be) experimenting with the silicone rubber that will soon mold the Gorgosaurus.

Dave writes: This is however, the end of the *preparation* series (hence the title) so we are rather drawing a line under this piece given that every practical part of the preparation has now been done and with Phil’s arrival the research phase of this specimen is beginning. While we will add more during he casting process, this is the end for now. We hope you have enjoyed this and any feedback on the series as a whole is most welcome. Thanks!

All photos here and in the series are owned by Darren Tanke and the Royal Tyrrell Museum.

Darren Tanke’s Gorgosaurus preparation 17: supporting the breaks

The last of the preparation is now being done on the Gorgosaurus. Several bones were completed on January 19th. These were the first ones to be completely finished. The nature of the rock is cracked and crumbly and despite best efforts, some rock along the edges and underneath the bones has fallen away. The bone is not properly supported and the missing rock needs to be replaced. The femur was badly affected this way. To remedy this (shown in a series of 4 pictures), I mixed some thick glue with sand from the Gorgosaurus block. Waste rock was broken up and ground into sand and dust, using a short length of a hardwood broom handle as a rolling pin. The resultant sand/dust was poured into the jar of glue and stirred together. The result was a thick paste which could be made more runny by adding more glue, or thicker by adding more sand. This paste was applied to the undercuts using a small metal spatula. Because the paste was so thick, it was easy to work and retained its shape. It dried hard in a couple hours and the bone is now safely supported. The support can be removed in the future if need be by squirting acetone onto it and removing the resulting paste. Also, once the paste is hardened, it can be shaped with an airscribe if needed. The final result is quite convincing as “real rock”.

The final treatment of the completed bones is a very thin coating of glue, made so thin that it does not sit on the bone surface, but soaks in. It seals up any remaining microcracks and dissolves and old glue on the surface. The provided picture with the brush shows part of the now fully prepared ischium, with the surface treatment of glue. Final preparation of the rest of the skull and skeleton will go quickly now.

All photos here and in the series are owned by Darren Tanke and the Royal Tyrrell Museum.

Darren Tanke’s Gorgosaurus preparation 16: more cleaning

Final work on the Gorgosaurus continues and I’m on track for being ready for the planned mid-February for molding of the specimen. At this stage, bare areas of the jacket are being glued and sand from the Gorgosaurus block sprinkled on to the wet glue to create “rock texture”. This is being done so the latex mold is of rock or simulated rock and not the bare plaster jacket. A few more belly ribs have also been found and most of the nice ilium uncovered. The ilium looked awful at first with a bad crack running through it but it has been saved. The attached pictures speak volumes as to how nice this specimen is. There is little more to show preparation-wise on this specimen (until the mold is started) so the future updates will be more photographic in nature as the specimen nears completion.

All photos here and in the series are owned by Darren Tanke and the Royal Tyrrell Museum.

Darren Tanke’s Gorgosaurus preparation 11: a hands-free glue system

This is an update for November 29-30. Work has slowed on the Gorgosaurus lately due to the labor-intensive amount of gluing that is required. Rock is still being removed, but at a much slower pace now. This update will once again focus on glue. Glues are so important due to the often badly fragmented nature of the fossil being prepared, its host rock, or both. An American vertebrate paleontologist told me decades ago: “If the was no such thing as glue, there would be no such thing as paleontology”. A bit of stretching the truth, but he did have a valid point. Glues in vertebrate paleontology are usually applied by brush or by an eydropper, though in some cases the fossil can be simply immersed. At times a specimen requires a lot of gluing, a job that takes many hours of work, sometimes stretching into weeks of dripping drop after drop of glue onto a specimen such as a dinosaur skeleton. [Dave notes: Glues can be a nightmare too if not used properly as this link explains].

Continue reading ‘Darren Tanke’s Gorgosaurus preparation 11: a hands-free glue system’

Gorgosaurs preparation review and Q & A

OK so last week Darren and I asked for questions about the preparation process and the Gorgosaurus project. Obviously Darren has way more knowledge and experience than me and is a researcher in his own right, but hopefully I can chip in on a few of these as well from the other side of things and my own experiences.

For those who are a bit late to the party, this is also an opportunity to round-up what’s been going on. Essentially Darren Tanke, a fossil preparator at the Royal Tyrell Museum in Canada is giving a blow-by-blow account and photo journal of his work on a new Gorgosaurus specimen. This started as a jacket of plaster collected in the field and Darren has been peeling away the rock to reveal the tyrannosaur entombed inside.

If you want to see how we got to where we are then you’ll want to see (deep breath): The introduction to Darren and Gorgosaurus, then Part 1, Part 2, Part 3, Part 4, Part 5, Part 6, Part 7, Part 8 and Part 9 and now here we are at the Q & A and prelude to, well Part X. Now onto the questions and our answers:

Continue reading ‘Gorgosaurs preparation review and Q & A’

Darren Tanke’s Gorgosaurus preparation 9: epoxy and a foot is found

This update covers November 17-18. There have been a major development on the Gorgosaurus project. Some people are having trouble figuring out how a femur could end up near the head so in this posting I include a rough schematic sketch I made on Nov. 17th showing the rough placement of known bones and presumed ones. When the drawing was done, the presence of a tibia and hind foot were not known but presumed- more on that later.

Work on the 17th confirmed the presence of a femur and fibula. The bone in both (femur especially) was well preserved in many places, but badly shattered, splintered and collapsed. Other places the bone is like a completely dried out chocolate cake and just as crumbly. It truly is awful bone to work on, but fortunately all the pieces are still in place or nearly so and the rock comes off the bone very well. In the last posting I briefly discussed 2 ton epoxy glue and in this posting I want to detail some common sense approaches and tricks I have used with epoxy glue in the past and have/will use on this Gorgosaurus.

Epoxy glue is typically mixed in a 50:50 ratio and has the consistency and viscosity close to that of honey. Techniques:

1. When using glue to fill cracks in bone or in the rock (or both), slowly pour the glue in at one end of the crack (usually the widest end) so it flows along driving the air in the crack ahead and out of the way. Simply pouring the glue into the crack can form large trapped air pockets of bubbles, weakening the join. Always pour at one end and let it flow along. If it is an angled but nearly horizontal crack, pour at the higher end, taking care that it does not flow out the lower end onto bone surfaces.
2. For a shallow pour, cram the bottom of the crack to the depth desired with packed tissue paper, then pour the glue in. Alternatively, you can mix the glue, wait until it begins to cure then pour the thickening glue into the crack. If the crack is two-sided with a vertical crack and a horizontal one, the poured glue will escape out of the vertical crack. Plug that off with tissue paper crammed in or use putty/plastecine to hold the glue in. I prefer the tissue paper technique.
3. If you find the epoxy too runny, you can thicken it up. Much like adding flour to gravy to thicken it, you can make the epoxy glue thicker by adding various inert materials. Materials such as clean sand, powdered glass (which may give the epoxy an unwanted white color), chopped strand (short lengths of fibreglass) can be mixed in. Another way to thicken the glue without adding other materials is to chill it in a fridge first, mix it up and then pour. It will still set, but will take its time doing it.
4. If you want the epoxy to be colored, the best way is to simply stir in powdered tempera paint until the desired color is achieved. The wet color of the paint/epoxy mix during the mixing phase may be different from the dry and hardened epoxy, so advance testing should be done.
5a. Epoxy, like any fluid, will follow the path of least resistance. If the glue is not flowing where you want it to, then raise the fossil or specimen jacket on one end and block it up with lengths of wood, or, being very careful,  tilt the table slightly. 5b. Another trick is to use your airscribe. Air blows out the tip. On a low setting, this air can be used to push around and steer the glue to places where you want it to go.
6. Epoxy curing is a chemical reaction, so if you want, a desk lamp can be aimed close to the setting glue and the warmth from the bulb help speed up the curing time. Don’t put the lamp too close- just close enough to keep the work area warm. This often works for other solvent-based glues too, especially those using acetone.

As with any new technique, test on a safe area first. Techniques 1,2, 5b, and 6 were used on the Gorgosaurus‘s knee region on the 17th. The glue cured overnight and on the 18th the rock airscribed away. This eventually resulted in epoxy glue “dikes” appearing atop the cracked (but no glue-filled) bones and this was simply airscribed away until near the bone. At this point a sharp knife (#15 scalpel blade) was used to shave and trim the excess glue away.

On the 18th, additional work around the fibula and cracked bone/rock there neccesitated my clearing a new work area. While brushing away loose matrix the extreme edges of three toe bones were found! These needed exposing and stabilizing so by the end of the day three complete toe bones and part of another were exposed. In one picture the plaster I poured in at the beginning of the project can be seen. It flowed deep into the smaller rock cracks and held the rock pieces together. These toe bones were exactly where I predicted they would be. No I don’t have X-ray vision, but this is where an extensive lab and fieldwork background comes in handy. Tyrannosaurids often pull their limbs up towards their body as part of their “death pose”. The legs fold up into a compressed “Z”, much like a scissors jack folded up. It is quite rare to find an articulated tyrannosaur femur and fibula together and not have a foot, so I was pretty sure the foot was there. The tibia is still unseen, but it has to be there- most of the foot articulates to it. Without the tibia being there, the foot would fall off. In the field, once we had the pelvis, I was pretty sure there was a skull, as the head is often pulled backwards over the pelvis (more of the “death pose” again). That prediction came true as well. Another thing I predicted this specimen might have was evidence of healing bite marks and it did; that prediction based on the fact about 50% of small tyrannosaurids from Alberta show evidence of this. So experience is invaluable in the field and laboratory when working on these remarkable specimens.

Work on the Gorgosaurus will likely slow down substantially now because the bone in the pelvic region appears to be very soft and crumbly, requiring much glue and glue drying time. Updates here may come now every 3-4 days, though I may fire off some brief fossil preparation tips from time to time. Don’t forget that the Royal Tyrrell Museum Facebook page has the daily preparation of this specimen posted there too, though postings there may slow down as well for the reasons above.

Note: Darren and I are still looking for questions on the specimen and preparation techniques , their effect on research etc. We’ll answer them later this week in a special post. Just leave your question as a comment below.

All photos here and in the series are owned by Darren Tanke and the Royal Tyrrell Museum.

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