TqB Posted October 12, 2014 Share Posted October 12, 2014 Here's a brief description of how I prepped the Yorkshire coast Palaeocoma milleri that won last month's invertebrate competition. It was found in the middle of the top face of large, hard sandstone boulder. The tide was coming in quite fast and I wasn't sure if it was extractable in time - but after a frantic hour of chiseling a channel around it it was ready to lift. Always a scary moment but the Estwing bolster did the job . The resulting block is 12" x 8" x 3". The curly arm on the left was loose and broken into four pieces - these were carefully packed and glued back on at home. The next step was to rough it out with an air pen and abrader to see how far the arms went. Sadly, none of the others were as complete as the exposed one but that's often the way with brittlestars... Also, the surface of the central area is slightly corroded by the acid from a decomposing thin layer of pyrite - a common problem from this formation. I also used some potassium hydroxide flakes which is why the matrix has turned red-brown along the top arms. Then more work with pen and KOH to expose the centre disc and bring out the arms: It was then soaked for a couple of days to remove KOH. After more penning and tidying with the air abrader, the pen marks were ground away and that's as far as I've taken it - there's certainly scope to do more but I'm leaving it for now. Tarquin Link to comment Share on other sites More sharing options...
Lmshoemaker Posted October 12, 2014 Share Posted October 12, 2014 Fantastic job with this, it almost looks alive. Link to comment Share on other sites More sharing options...
snolly50 Posted October 12, 2014 Share Posted October 12, 2014 Wonderfully done! Human beings, who are almost unique in having the ability to learn from the experience of others, also are remarkable for their apparent disinclination to do so. - Douglas Adams, Last Chance to See Link to comment Share on other sites More sharing options...
fossilized6s Posted October 12, 2014 Share Posted October 12, 2014 Thanks for posting your prep journey! It is a amazing piece sir! ~Charlie~ "There are those that look at things the way they are, and ask why.....i dream of things that never were, and ask why not?" ~RFK ->Get your Mosasaur print ->How to spot a fake Trilobite ->How to identify a CONCRETION from a DINOSAUR EGG Link to comment Share on other sites More sharing options...
Ramo Posted October 12, 2014 Share Posted October 12, 2014 That is awesome! Does the KOH work to soften the matrix? If so, how deep in the rock does it work? Ramo For one species to mourn the death of another is a new thing under the sun. -Aldo Leopold Link to comment Share on other sites More sharing options...
TqB Posted October 13, 2014 Author Share Posted October 13, 2014 (edited) Thanks, everyone! Ramo - KOH works when there's enough clay in the matrix - you place pellets or (in this case) flakes on the surface and allow atmospheric moisture to dissolve them; the highly saturated solution is absorbed by clay particles up to several mm deep in the rock, swelling it up and loosening it. It takes a few hours and can then be washed away, with gentle brushing. It's a method that has to be used with care - it can all too easily break up the specimen, especially with complex structures like articulated echinoderms - crinoids in particular are easy to destroy this way. And often it doesn't work at all - there are areas of this one that it had no effect on, the fossil being mainly in a thin shale lens but penetrating in places to the overlying sandstone. I mentioned acid from the pyrite content (a hard thin layer which had to be mechanically removed) - KOH has a useful side effect of helping to neutralise it but I still soaked it in water for a couple of days afterwards. Edited October 13, 2014 by TqB 1 Tarquin Link to comment Share on other sites More sharing options...
RJB Posted October 13, 2014 Share Posted October 13, 2014 Super job. I can only imagine the fun, the anticipation and the satisfaction. Very nice specimen. RB Link to comment Share on other sites More sharing options...
Fossildude19 Posted October 13, 2014 Share Posted October 13, 2014 Thanks for posting the process, Tarquin! A truly worthy Fossil of the Month. Regards, Tim - VETERAN SHALE SPLITTER VFOTM --- APRIL - 2015 __________________________________________________ "In every walk with nature one receives far more than he seeks." John Muir ~ ~ ~ ~ ><))))( *> About Me Link to comment Share on other sites More sharing options...
Roz Posted October 13, 2014 Share Posted October 13, 2014 Just beautiful! Welcome to the forum! Link to comment Share on other sites More sharing options...
Triceratops Posted October 17, 2014 Share Posted October 17, 2014 Great fossil and great prep. Congratulations! -Lyall Link to comment Share on other sites More sharing options...
TqB Posted October 18, 2014 Author Share Posted October 18, 2014 Thanks again for the kind comments, everyone . Tarquin Link to comment Share on other sites More sharing options...
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