So, some of the glass cast hearts are out of the kiln now, and a comment from Rosie (thanks Rosie!) made me realize that I hadn't taken photos, so I did so right away. Otherwise they would be sold, and I wouldn't have a record.
The first batch came out well - but not excellent. I have a pretty good idea why: I cast RTV 'positives' out of the plaster negatives, so when I went to kiln wash the molds (to stop the glass from sticking) there was a residue in the mold, and the kiln wash wasn't keen to adhere to the plaster. Tomorrow I will make more plasters - to cast more, and these should be nice and clean.
The effect on the glass is that is is not as crystal clear as I would like it, so we'll see what the next batch looks like.
On friday and saturday I got to blow some glass, so next time I'll show you what I made.