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A few months ago I started to prepare this specimen which we collected five or so years ago near Wee Jasper, NSW. Specimens from this site must be acid prepared since they are encased in a hard limestone, making mechanical preparation impossible. Included will be my method for preparing this specimen, as well as my mistakes! Placoderm fossils from this site are typically found as black cross sections, just like the pictured specimen. Bone can be distinguished from other fossils in most cases due to the bumpy texture present on the exterior surface. To consolidate the specimen before working on it, I applied very dilute paraloid-b72 to the bone. At this stage, a dilute solution is best to ensure the paraloid can penetrate as deep into the bone as possible. If the ratio of paraloid to acetone is too high, the solution will be too viscous and the paraloid will only coat the surface of the bone. Next, I air scribed the bulk of the matrix I wanted to remove in order to greatly speed up the process. Here is the specimen after a couple of baths in 8% acetic acid (double strength store bought vinegar): Between acid baths, I let the specimen soak in water for a couple of days to remove any residual vinegar and prevent the build up of crystals which may form inside the bone and damage it once it dries out. Once dry, I applied more of the dilute paraloid to the freshly exposed bone with an eye dropper, making sure the bone was soaked and well consolidated. A photo showing matrix carefully removed with an air scribe between acid baths: I think it was around this point I made a very annoying and easily preventable mistake - I broke the fossil while moving it. It was easy to glue the pieces back on with a stronger, more viscous solution of 20% paraloid but now there are some ugly cracks through the specimen in places. I opted for paraloid instead of superglue because it is easily removable, if I'm not satisfied with my reattachment I just have to apply some acetone and the glue will dissolve again. I broke a couple of other pieces off too which is incredibly annoying, fragile fossils and I don't tend to mix well! Here are some photos of the finished specimen: Note the cracks on the right side of the specimen in this photo. I can't remember how I broke so much off at one time but it is incredibly annoying and so easily avoidable! The fracture towards the left side of the specimen here is natural, it may have been filled in by a band of silica which makes up much of the remaining rock. The crack in this photo was a natural fracture, but it looks like a larger chunk of bone fell off when I was gluing it back together before I started the acid preparation. This photo was taken at almost same angle as the "before" photo below it for reference! Here it is easy to see where the blueish limestone dissolved away, leaving only the bone and the bands of silica which make a convenient stand and support for the fossil. Thank you for reading:)

Any suggestions on this tiny bone? I found it while dissolving chunks of matrix from the lower Cretaceous Mackunda Formation collected in western Queensland, Australia. The matrix is rich in shells, crustaceans, fish and shark teeth but terrestrial species are known from the formation. It doesn't look like any of the fish bones I've seen from here so am considering bird? They've been found in the neighbouring Toolebuc Formation by @Mike from North Queensland so it seems possible! Thanks for any input:)

Beasley, C., Parvaz, D.B., Cotton, L. and Littler, K., 2020. Liberating microfossils from indurated carbonates: comparison of three disaggregation methods. Journal of Micropalaeontology, 39(2), pp.169-181. (Researchgate PDF) Version 2 of Beasley et al. (2020) Yours, Paul H.

Hello, i have a few fossils like the one in the picture, they are all shells in limestone. I want to clean them and i have had some success with acetic acid. I just wondered if someone had any tips or a better way to clean them, also if anyone knows whats the best concentration to clean them, mine is 25% acid but this seems a little high. I can post a picture of a relatively clean one if it helps to identify the best way to clean them.