Trilobite Repair - Casting from the imprint

[Calico Jack]

I'm a fairly novice preparator and I was wondering if some of you more experienced folks could help me out a bit.

 

I am working on a dipleura that unfortunately broke apart upon extraction. Some fragments of the pygidium were lost. I have the imprint and was considering casting the missing parts in plaster or something ideally reversible. My goal is to turn this fossil into a nice display piece. There are also some large voids in the matrix I would like to fill in. I've never done anything of this sort to a fossil before and I was hoping for some guidance on materials, techniques, etc.

 

I have attached a couple of photos of the areas I would like to repair. 

[Wrangellian]

Plaster sounds like a good idea. I have not tried it, and can't think of anything better (I have tried cement but it doesn't dry very hard unless it dries slowly). Probably someone else will come along with better advice.

[Kane]

For the trilobite itself:

 

You might consider a two-part epoxy like Milliput. Go for a fine white, which you can shape and smooth in the cracks while wet, let it cure for 6+ hours, and then you can abrade or sand it to the perfect shape and contour. After that comes colour matching with a water-based acrylic paint. If you don't like the look of it, it is reversible by using acetone and some scribing or picking off. 

 

One great tip another forum member, Malcolm, gave me that would apply here is to use plastic cling wrap to smooth the Milliput by stretching it over the area while wet. 

 

The one thing I could see being a challenge is how to replicate the dimpling microsculpture pattern.

 

For the missing chunk of matrix:

 

That may need a different approach than the epoxy, for sure. I've never attempted matrix restoration, but I've read that it involves pulverizing some matrix, mix with water and glue. I'm going to tap my prep mentor on this: @Malcolmt

[Calico Jack]

Thanks @Kane I'll try the Milliput. I was thinking that maybe I could fill in the crack let it cure a bit and then press the imprint onto it to restore the dimpling pattern. For the missing matrix, I think I have too large a void to fill with matrix and glue alone. Perhaps I can fill it in with plaster and then apply a top coat of glue/matrix? Thanks so much for the advice!

 

-Jack