This is my first attempt at casting and I obviously have a lot to learn.

I was disappointed that the resin didn't do what is was supposed to do, that is, expel all bubbles. It looked good when in the mould but there are thousands of tiny bubbles.

This was cast in two layers. The first layer was left to cure for 12 hours, as suggested by Warren. The broken T was then pressed into the resin and the second layer poured. What was surprising was that, although the resin was very stiff by this time, the T kept trying to float to the surface and had to be continuously pushed back down using a thin needle. Eventually the resin cured enough to secure the T but it was still closer to the surface than I wanted.

What have I done wrong or not done so as to have so many bubbles? I mixed the resin carefully with a slow stir. I ran a heat gun over both layers.  Difficult to see in the photo but there are thousands of micro bubbles in the resin. The face adjacent to the plaque is polished but the others are sanded to a matt finish.