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It's the silicified bits that etch out.
Edited by TqB 2015-05-21 08:41:43
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Just thought I'd post these up in case anyone was going to prep anything in limestone using acid (you can learn from my mistakes haha) I've been using either acetic acid (pickling vinegar) or dilute hydrochloric acid (high strength brick acid) either bathing the specimens or using a burette to run a controlled drip onto the specimens.  Unfortunately some of the most impressive specimens have sold an I forgot to take pics of them but here are a few in progress and before/after pics for anyone interested:

This is a little nugget of Dibunophylum which i mostly cut out using a dremel, glued it back together and then bathed in vinegar overnight, cleaned it off this morning and then back into fresh vinegar so hopefully will be lovely by the time i get home from work tonight.



Next is a complete pebble from weardale which i put into vinegar overnight just to clean it up:



Next is a large lump of limestone which obviously had a lot of fossil in it, i bathed it in the brick acid overnight and was very pleasantly surprised by the results:



The last peice is something im working on with alternatively removing matrix with the dremel and then either bathing or dripping acid onto the matrix, there are some large sections of coral within it and id like to expose as much as possible whilst keeping enough matrix to make the specimen stand up:



and lastly a few little tips; the brick acid is very corrosive and will eat away the fossils as well if they are lft in it too long, some limestone seems to polish to a shiny black whilst other stuff goes very matt and grey and lastly if you do prep using pickling vinegar your specimens will stink of vinegar for a very long time!


I hope someone gets some use from this, its the first hints/tips thing iv postedConfused
I aint got time to bleed!
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Impressive! So why doesn't the acid damage the fossils?
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The acid will damage the fossil - but it eats the fossil far slower than the matrix.

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