Crab preparation (How to fill cracks to apply paraloid?)

[pochoclo666]

Hello everyone ! I have stored these crabs a couple of years ago, while storing them they cracked (I suppose it is due to the internal humidity, they were found on a sea coast). I have the paraloid to apply them, but there are these cracks that I have to fill somehow so the paraloid doesn't leak. What material do you suggest as filling? And please know what percentage of acetone and paraloid is in the mixture? Thank you all ! greetings !

 

ps: the material that covers the crabs is hard sand

 

EDIT: The reality is that I don't have much of an idea of how to prepare them, I was thinking of applying a layer of paraloid on one side, also filling in the cracks on something (the one where the broken crab can be seen, the place where it was exposed) and working on it on the other side.

 

 

Edited April 17 by pochoclo666

[Thomas.Dodson]

Paraloid itself can be used to fill in the cracks, just use more paraloid to acetone. The easiest way is probably to use super glue, it is quick and cheap.

[oilshale]

You can use Paraloid but cyanoacrylate is better in my opinion. 
If you want the Paraloid to penetrate the cracks well, the solution must be low viscosity - so little Paraloid resin and a lot of acetone (for example 5% Paraloid). When drying, the acetone evaporates and the Paraloid remains in the cracks. The cracks are therefore never completely filled with solid Paraloid resin - only 5%. Even if you repeat this several times, it won't get much better.
If you use a higher concentration of Paraloid (say 30%), more resin is transported into the cracks and remains there after the acetone has evaporated - but only 30% of the volume of the cracks is filled with resin. On the other hand, the solution becomes highly viscous and therefore does not penetrate the cracks as well..
Cyanoacrylate has a low viscosity and shrinks only minimally during curing - it contains no solvent. The cracks are almost 100% filled with resin.

 

[Ptychodus04]

I would not recommend cyanoacrylate, unless you're ok dealing with matrix adhered to your specimens. It will soak into the matrix and bond it to the crab, makaing preparation very difficult.

 

Mix up a thin solution (roughly 5%0) of paraloid and pour it into the cracks. Then take a thicker solution (consistency of warm honey) and pour it into the cracks. It's going to leak out but it will lock everything together. If your blocks need to be stabilized, you can go about it 2 ways, 1: direct application of thin paraloid to the back until it is hard enough to hold together. 2: make a 1/2 jacket with plaster and burlap to cradle the back of the specimen.

[oilshale]

I am not familiar with your matrix. Cyanoacrylate might create a problem if the matrix / fossil is very porous ( but I never experienced a problem unless it is a very porous diatomic matrix).

Edited April 18 by oilshale

[Ptychodus04]

1 hour ago, oilshale said:

I am not familiar with your matrix. Cyanoacrylate might create a problem if the matrix / fossil is very porous ( but I never experienced a problem unless it is a very porous diatomic matrix).

 

The matrix is compacted sand. Cyanoacrylate will soak into this like a fiend.

[pochoclo666]

20 hours ago, Thomas.Dodson said:

Paraloid itself can be used to fill in the cracks, just use more paraloid to acetone. The easiest way is probably to use super glue, it is quick and cheap.

 

What proportions of paraloid and acetone do you recommend to make a thin layer that gives consistency to the damaged side of the fossil? (it is broken, it is missing pieces of fossil, the side that is covered is healthy) so I put a layer on it to give it hardness on one side, so I can work on it without fear of it breaking.

[pochoclo666]

21 minutes ago, Ptychodus04 said:

 

The matrix is compacted sand. Cyanoacrylate will soak into this like a fiend.

 

What proportions of paraloid and acetone do you recommend to make a thin layer that gives consistency to the damaged side of the fossil? (it is broken, it is missing pieces of fossil, the side that is covered is healthy) so I put a layer on it to give it hardness on one side, so I can work on it without fear of it breaking.

Edited April 18 by pochoclo666

[Ptychodus04]

2 minutes ago, pochoclo666 said:

 

What proportions of paraloid and acetone do you recommend to make a thin layer that gives consistency to the damaged side of the fossil? (it is broken, it is missing pieces of fossil, the side that is covered is healthy) so I put a layer on it to give it hardness on one side, so I can work on it without fear of it breaking.

If the broken side is the one that will not be prepped, use a solution of 2-5% to consolidate the matrix. 

[pochoclo666]

8 minutes ago, Ptychodus04 said:

If the broken side is the one that will not be prepped, use a solution of 2-5% to consolidate the matrix. 

 

thanks for answering ! Would it be a solution of 5% paraloid and 95% acetone? Would it be very liquid? apply super glue to the crack to fill and join, will the paraloid dissolve it and ruin the fossil, dissolving the glue that is in the crack and getting inside?

[Ptychodus04]

59 minutes ago, pochoclo666 said:

 

thanks for answering ! Would it be a solution of 5% paraloid and 95% acetone? Would it be very liquid? apply super glue to the crack to fill and join, will the paraloid dissolve it and ruin the fossil, dissolving the glue that is in the crack and getting inside?

Your math is correct. 5% Paraloid B72 and 95% acetone. The ratio does not need to be exact. I would not use cyanoacrylate for the crack repair unless you're ok with dealing with the matrix being glued to the specimen. 

 

Local application of paraloid won't adversely affect your glue joints.