I was recently on a school field trip with my boys. While away, we picked up a pair of fossilized scallop shells, top and bottom. I plan to embed these in a clear, colourless resin, then mount them in a two
2-3" rimu slabs, with the top slab at about a 45 deg angle to the base, mimicing an open scallop. I'm looking for some advise on a good embedding resin to mount these in. I'm planning to brush in the first few coats as the shells are rough, and I think will trap air bubbles, which will detract from the whole look I'm trying to achieve.
Water-clear polyester embedding resin. You need to use the right resin, but anywhere selling fibreglass supplies should have it.
It's usual to pour one layer first to form a "bed" then cure it overnight. Lay the object on top in a position that allows it to vent air bubbles, then pour the second layer over it. Carefully pour the resin first into the voids to fill them. Use a wire to tease out any visible bubbles. Getting the orientation right is usually enough to avoid bubble problems. It doesn't matter which way is "up" if you're going to polish the surfaces afterwards,
You can also tint the resin to make an opaque background (usually poured last). Back in the '70s we'd embed seaweed or anything alongside shells.
Paper should be sealed with hairspray first, otherwise it tends to go translucent.
The resin cures tacky if exposed to the air, so either cover it with polyester (Mylar) sheet, or do some sanding. It'll sand easily enough with normal abrasives. Use silicon carbide wet and dry down to about
2000 grit (used wet) to get it clear, or else about 800 grit and then paste polishes. Use a powered sander for this, because life's too short to do this job by hand!
Moulds can be bought or made of anything with a good surface, even silicone rubber. Candle moulds can work, but natural rubber ones need careful waxing. You can even use one-off moulds in Plasticine. MDF with a few coats of shellac is good, then apply proper release wax (from the fibreglass supplier) before pouring. Rough surfaced moulds just need the cast polishing afterwards, which is no big deal if you're already doing the air-exposed surface.
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