Partial Ichthyosaur Paddle Acid Preperation

[LiamL]

Here is a section of Ichthyosaur paddle that I found recently near Whitby.

 

The sea has rounded the pebble nicely but there is still a little bit of matrix to remove. I tried using my air pen to remove the matrix but unfortunately it's like penning metal due to the pyrite.

So acid is the only option.

 

The first dip I only protected with paraloid for a quick dip (1Hour) which worked well and gave the bones some definition. 

 

 

 

On the second dip today, I coated the exposed bones with some candle wax to give them some added protection against the acid.  

I did a longer dip, and a little more bone has been revealed but not much. I think it might be a long process with this one.

 

For people who are familiar with acid prep, do you remove the wax each cycle? It seems counter productive as it is still protecting the bone and has not been eaten away.

 

More pictures to follow soon.

 

[pachy-pleuro-whatnot-odon]

I've never done acid preparation myself, but I wouldn't remove the wax after each cycle. Just rinse and apply new. You can always remove the excess wax once the bone has become fully exposed. And when it comes to that, I wonder whether the acid would be able to eat away at the pyrite you mentioned. Otherwise, how would it expose the bone underneath?

Edited March 25, 2023 by pachy-pleuro-whatnot-odon

[mamlambo]

@LiamL A few things I've learnt from trial and error:

1. Acid can work itself in under the wax which won't be visible from the outside. This happened to me when I was testing it out so it's good to remove it every few round and reapply the B72. My preferred method is to not use wax and rather reapply the B72 as I can then be sure I'm covering all the bone but I've seen good results with the wax as well. I use a thin B72 first and then a thicker one. The thin B72 penetrates better into the bone.

2. The exposed cancellous tissue (honeycombing) is the most susceptible to acid, in my rocks anyway, as they have calcite infill which the acid just loves. If the bone has the outer surface present it's much more resistant to the acid.

3. Multiple short baths gives me better results than a few long baths.

4. I gently brush the silt away with a very delicate toothbrush every 10 minutes as that exposes the fresh matrix underneath, otherwise it forms a barrier to the acid.

5. After each acid bath I put it in a very large tub of fresh water for a day and I change the water out at least once. Ideally rinse the fossil after the acid under a running tap for a couple of minutes before putting in the water bath, this gets rid of the vinegar on the surface.

This is what works best for my mudstone concretions, results may vary with other matrixes!

[LiamL]

2 hours ago, mamlambo said:

@LiamL A few things I've learnt from trial and error:

1. Acid can work itself in under the wax which won't be visible from the outside. This happened to me when I was testing it out so it's good to remove it every few round and reapply the B72. My preferred method is to not use wax and rather reapply the B72 as I can then be sure I'm covering all the bone but I've seen good results with the wax as well. I use a thin B72 first and then a thicker one. The thin B72 penetrates better into the bone.

2. The exposed cancellous tissue (honeycombing) is the most susceptible to acid, in my rocks anyway, as they have calcite infill which the acid just loves. If the bone has the outer surface present it's much more resistant to the acid.

3. Multiple short baths gives me better results than a few long baths.

4. I gently brush the silt away with a very delicate toothbrush every 10 minutes as that exposes the fresh matrix underneath, otherwise it forms a barrier to the acid.

5. After each acid bath I put it in a very large tub of fresh water for a day and I change the water out at least once. Ideally rinse the fossil after the acid under a running tap for a couple of minutes before putting in the water bath, this gets rid of the vinegar on the surface.

This is what works best for my mudstone concretions, results may vary with other matrixes!

Your video is helpful, i’ve rewatched it afew times over the last weeks. Cheers for the tips!

Edited March 25, 2023 by LiamL

[LiamL]

15 hours ago, mamlambo said:

@LiamL A few things I've learnt from trial and error:

1. Acid can work itself in under the wax which won't be visible from the outside. This happened to me when I was testing it out so it's good to remove it every few round and reapply the B72. My preferred method is to not use wax and rather reapply the B72 as I can then be sure I'm covering all the bone but I've seen good results with the wax as well. I use a thin B72 first and then a thicker one. The thin B72 penetrates better into the bone.

2. The exposed cancellous tissue (honeycombing) is the most susceptible to acid, in my rocks anyway, as they have calcite infill which the acid just loves. If the bone has the outer surface present it's much more resistant to the acid.

3. Multiple short baths gives me better results than a few long baths.

4. I gently brush the silt away with a very delicate toothbrush every 10 minutes as that exposes the fresh matrix underneath, otherwise it forms a barrier to the acid.

5. After each acid bath I put it in a very large tub of fresh water for a day and I change the water out at least once. Ideally rinse the fossil after the acid under a running tap for a couple of minutes before putting in the water bath, this gets rid of the vinegar on the surface.

This is what works best for my mudstone concretions, results may vary with other matrixes!

 

Using  a toothbrush to brush away the sludge during the dip is an interesting idea. I will try that in my next dip.

Many thanks!

[pachy-pleuro-whatnot-odon]

9 hours ago, LiamL said:

Using  a toothbrush to brush away the sludge during the dip is an interesting idea. I will try that in my next dip.

 

It is, in fact, also something I do when treating smaller specimens to an acid bath: soak, brush, rinse, neutralise, repeat...

[LiamL]

On 3/26/2023 at 8:52 AM, pachy-pleuro-whatnot-odon said:

 

It is, in fact, also something I do when treating smaller specimens to an acid bath: soak, brush, rinse, neutralise, repeat...

 

If you notice a specimen is going slow with little to no change do you either increase the acid time, or make it stronger?

 

[pachy-pleuro-whatnot-odon]

1 hour ago, LiamL said:

If you notice a specimen is going slow with little to no change do you either increase the acid time, or make it stronger?

 

That's what I would expect with the pyritic content in the rock, to be honest. Acid won't attack the pyrite. That is, I'd expect you to at one point get stuck on only pyrite remaining, therefore progress halting. I think - but, again, there'll be more knowledgeable people out there - you might, at this point, need to switch to mechanical preparation, sandblasting with a hard medium in particular...