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I recently decided to try a new (for me) method of preparation which involves dissolving away bone in hydrochloric acid. This method was used on the specimens published in various papers on the Hunter Siltstone, an important Devonian fish locality in NSW. Fossils are dissolved in hydrochloric acid, leaving an impression of the bone which is then cast in latex and/or resin. This method is used because the rocks tend to split right through the bone itself, so you miss a lot of the features present on the exterior. After a cast of the specimen is made, it can be coated in black ink and photographed with a coating of ammonium chloride so all the details are clearer. Here is the specimen I decided to try - a partial acanthodian jaw. This is what it looked like as split, just a cross section of the bone. The first step is dissolving away the bone in hydrochloric acid. I don't have any photos of this step but I just used a store bought bottle I had laying around, not watered down or anything. I think it took 2-3 days for all of the bone to dissolve away on this specimen. Keep in mind hydrochloric is nasty stuff, definitely best to wear gloves, avoid splashing it and use it in a well ventilated space! After leaving the rock to soak in water for a few days after the acid bath, I was ready to make a latex cast of the impression. The first coat of latex should be super thin to ensure as much detail as possible is captured. After the second or third thin layer, I started to apply thicker layers. The latex I used ended up being from 1999, it was only bought a few years ago so mustn't be in very high demand! Here is a photo of the latex cast and the finished specimen. In the second photo I applied a coating of indian ink for good contrast when I eventually applied ammonium chloride for photography. This was my first time using ammonium chloride so it took a lot of attempts before I was happy with my results. I'm still a bit unsatisfied, not sure if it's because of the ammonium chloride itself or if it's just showing up imperfections in the cast more. This ended up being an ischnacanthid acanthodian jaw, either Grenfellacanthus or something new. Have linked the Grenfellacanthus paper here for those interested: LINK
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Just got back from a 5 day trip to western NSW where we visited a number of sites, some of which we had not visited before. Will post more photos and information over the next few days as I have a lot to photograph, but here are some field shots from day two (our first collecting day)... Our first site was located near Grenfell and is known for its excellent Devonian fish fauna, including placoderms and sarcopterygians. While not as well preserved as the nearby Canowindra site, these are collectable which is a start . We were only given a vague site on a hillside located on private property, so once we had permission to access the site the next issue was finding where the fossil bearing layers were. This involved climbing a very steep hill and breaking open any rocks we saw, and after finding evidence of placoderm plates the next task was to figure out where they originated. A number of fossil bearing layers were found and it seems the material is very extensively distributed, presumably occurring throughout the surrounding hills as well. Here are some photos of one rock face we worked and the terrain - There were a number of rocks with exposed fossils on them, for example this one which is covered in ornamentation from placoderm plates. And here is a field photo of a partial Sarcopterygian(?) jaw, my thumb is on the left for scale.