Recipe for fixing brittle matrix (Mosasaur Kem Kem fossil)

[Flx]

Dear fossil preparation experts,
I recently acquired a series of articulated vertebrae of a Mosasaur in it's original matrix. The fossil is coming from Kem Kem region in Morocco.
My goal is not to extract the fossil bone from the matrix. This would be quite difficult due to the fragility of the specimen. Instead, I would like to clean up the matrix to make it look nicer.

 

Now, my problem is the following:
In some areas the matrix is quite dense and hard. In some other areas it is extremely brittle (almost like sand). I would like to use this original matrix-sand to repair the matrix in some spots. I was thinking about mixing the sand with liquid (water? glue?) to get a material that I can use for re-modelling the damaged matrix. Does someone have a good recipe for that? 

 

Thank you.

[izak_]

Im no expert but you might be able to use controlled amounts of vinegar and a toothbrush. You could use something like a pipette to apply vinegar in areas around the bone, scrub, then was it off with water. This works for me in similar matrixes. And thats just for the cleaning up bit, and maybe don't scrub the matrix with vinegar as it creates weird lines, only clean bones that way. Also don't do it until an expert gives their advice

 

Izak

Edited June 22, 2017 by izak_
Reasons

[Ptychodus04]

Is the matrix so brittle that preparation could cause the specimen to break?

 

If this is the case, encase it in a 1/2 field jacket to hold it together. Turn the piece upside down and coat it with layers of burlap strips soaked in plaster. Allow this to completely dry and you will have a very stable specimen to prepare. You can leave the specimen in the jacket forever. It can be trimmed and stained to clean it up.

 

Another option is to heavily consolidate the matrix with Paraloid, Butvar, or Vinac. Do this from the back as well. This process will take a few days to complete. All ratios are acetone:plastic by volume and are approximate.

 

Srart with a single coat over the whole back of the piece with a thin solution for deep penetration (50:1)

 

Then progress to two coats of thicker solution (30:1 or even 20:1). Allow this to dry for several hours and check for stability. This should significantly harden the matrix. If it is still brittle, apply more of the thick solution until you are happy with the stability. This will impart a somewhat shiny finish to the specimen. If this is indescribable, you can swab the surface with acetone to remove the plastic from the outer surface of the matrix to reduce the sheen.

 

Now, in to the matrix repair. You can mix your loose sand with your plastic solution for the matrix repair. This will glue it in place well. 

 

If you are crack filling, I like to cram as much loose matrix into the crack and the drip 50:1 solution on it. Then I drop some 30:1 solution on it and sprinkle dry matrix in top so it sticks in the wet adhesive. This keeps the repair from looking like it was put in with a putty knife.

 

While you prep, coat exposed bone with 50:1 solution and when you are done, give the whole piece a coat of 50:1. This will give you a well stabilized piece that will last forever.

[Flx]

Thank you very much for the helpful information.

Luckily, the fossil/matrix is already embedded in a plaster field jacket on the backside. Otherwise transporting the fossil by air freight would have been impossible I think. 

I will try your polymer-acetone solution coating method for stabilizing and re-building the matrix on the frontside.