The sea biscuit (not the horse, the shell) had the same problem as the pink umbonium shells — it floats. I came back to my resin 8 hours later to find the sea biscuit trying to escape. The red stuff was some sponge that washed ashore. It was velvety red when I found it. Drying in the sun, it got a little dull. The resin brought back the wet color.