Fossil crab

[fgiarro]

Hello. I acquired a crab fossil (Harpactocarcinus punctulatus, Eocene, Italy). The fossil still has a whitish matrix patina that covers the back of the exoskeleton (and other parts). I think it's possible to carry out further preparation of the fossil to highlight the structures of the back - I have no experience in this regard but I am curious to know if it is possible (and/or advisable) to prepare the fossil with simple mechanical (or chemical) methods, since I don't have a sand blaster system. I attach 3 images of the fossil. Thanks in advance, Fabio

[Shellseeker]

Welcome to the fossil forum.  I'll "flag" a couple of Crab and/or prep experts:  @RJB, @Ptychodus04

[Huntonia]

I'm certainly no expert but most things can be prepped with simple mechanical tools with enough patience. However from what I've heard crab concretions are very hard so it may require a lot of patience. No idea what chemical methods would do, from what I hear they're typically used on soft limestone type matrixes. I think that something strong enough to eat away at crab matrix could quite possibly risk ruining the crab. However, I'll say it again, I'm no expert, wait for those who are to voice their more educated opinions.

[Ptychodus04]

I would start by lightly scrubbing the exposed shell with a toothbrush soaked in ethanol or acetone. This will soften the matrix a bit without soaking the crab with water and possibly destroying it. Ethanol will give you a bit more working time and isn't as offensive to the nose as acetone is.

[caldigger]

On 2/4/2020 at 12:10 PM, Ptychodus04 said:

Ethanol will give you a bit more working time and isn't as offensive to the nose as acetone is.

Having worked on petroleum/ethanol tankers I find it just the opposite. But to each his own.

I can work around Acetone all day, but get me around ethanol fumes and I get nauseas within seconds. 

[Ptychodus04]

6 minutes ago, caldigger said:

Having worked on petroleum/ethanol tankers I find it just the opposite. But to each his own. I can work around Acetone all day, but get me around ethanol fumes and I get nauseas within seconds. 

I find acetone to be more offensive but I typically have a respirator on when I'm working so I don't smell any of them regardless.

[fgiarro]

Thanks for replies- I tried with a toothbrush soaked in ethanol and after in acetone, but neither method is effective in eliminating the whitish matrix. Maybe that's too hard for those solvents and needs a stronger chemical treatment

[Ruger9a]

Very nice acquisition!!!!  Thanks for sharing.  Definitely post the results of your prepping effort.  I have only prepped 5 or 6 crab fossils and the matrix was very hard.  I took my time using only an engraving tool and blade tips.  It was very tedious but well worth the results - to me anyway.  I still have a few unprepped crabs that I just can't seem to start on once I considered the extensive time frames involved with prepping the others.  Good luck in you efforts, be patient and please keep us posted (with photos).

[Ptychodus04]

2 hours ago, fgiarro said:

Thanks for replies- I tried with a toothbrush soaked in ethanol and after in acetone, but neither method is effective in eliminating the whitish matrix. Maybe that's too hard for those solvents and needs a stronger chemical treatment

You can test a bit of the matrix to see if it responds to acid. Drop a small bit of vinegar on it and see if it bubbles. If so, you can acid prep it but be very careful as the acid will attack the shell as well as the matrix.

[caterpillar]

Try to brush the crab with white vinegar (8°). But don't dip it in.

Then rinse well with water

[crabfossilsteve]

Personally, I think the white on the carapace shows the details nicely.  If you wanted to show more details of the crab, you could use dental picks or pin vise to scrape more matrix off around the claws and the edges of the carapace.  As indicated, vinegar might loosen up some of that matrix on the crab though, but experiment in small areas first. Rinse well.

 

Good luck and nice crab.

[fgiarro]

On 6/2/2020 at 6:57 PM, crabfossilsteve said:

Personally, I think the white on the carapace shows the details nicely.  If you wanted to show more details of the crab, you could use dental picks or pin vise to scrape more matrix off around the claws and the edges of the carapace.  As indicated, vinegar might loosen up some of that matrix on the crab though, but experiment in small areas first. Rinse well.

 

Good luck and nice crab.

Thank you all for the answers- I think I'll follow crabfossilsteve's advice, also because the white vinegar (I used 8% acetic acid) has failed, the hard matrix didn't soften and remained on the fossil- Thanks Fabio