Fusing Glass to Cement in a Kiln

Plaster of Paris is used to make molds. It is all so used in those same moulds to make all kind of decorative items. These decorative items are painted with glazing paint that form a glossy glass layer on the outside after being fired in a kiln. The glazing paint can be used of clay earthenware or fine china to give it a glossy glass surface.

Thanks for the info. I'm actually looking to use the cement/concrete item as the finished product but with some glass accents. I'd prefer to form the glass accents to the concrete item instead of imbedding them into the wet concrete.

Would a salt glaze work?

One problem with your idea is the temp. ranges of the two materials. Glass is workable at 1600-2000+ degrees and normal concrete can't handle any where near this temp. One alternative is to use a high temp refractory instead of concrete but this would probably be to expensive. The next problem is the two materials have a very different COE and when it all cooled the glass would crack or break out most of the time. If you are thinking about melting glass onto the concrete I would suggest boro-silicate glass because it can handle the quick cooling caused by putting hot glass onto warm/cold concrete better than the other types of glass. You might could cast a groove or dovetail impression into the concrete that would help hold the borosilicate after it cooled. The problem with this idea is that dropping hot glass onto the concrete will tend to make it "pop" or spall out from the moisture trapped inside the concrete expanding into steam when it heats up. You may can preheat the concrete so this water moisture will evaporate before you put the hot glass on it. This is one of those things that needs allot of experimenting with to really know what will work if anything does. If you are planning to play around with this idea please be careful and wear flame retardant clothing, gloves, safety glasses and other PPE for the job. Hot glass and concrete can wreak havoc on flesh, hair, eyes etc.