Thompson enamels makes lead free glass products in various particle sizes for metals and glass. I use the medium temperature-low expansion enamels for window glass and 400 series stainless steel. The coefficent of expansion is 80-83 so these enamels should still be pretested on your recycled glass.
Although I had used window glass compatible colored frit as a top surface accent in my castings, it did not show up as well as I wanted on the darker glass (dark green and black glass). So I decided to add more of a lighter or whitish look to distinguish the wings from the body. I also added enamels to brighten the color of the bodies.
Process wise, I buy the powdered form of the enamels and sprinkle it fairly heavily on the top of a sandblasted and sanded dragonfly casting. Since I am refiring a finished casting, it must be fired extremely slow up to around 1360 degrees or it will crack. I am using a schedule of 50 degrees per hour, hold for an hour or more at 1100 degrees, 60 degrees per hour to 1350 and hold for 5 minutes and then back down at the same rate (and hold again at 1100 degrees for an hour or more). **Remember that kilns can vary temperature wise and so can the size of the glass casting, so the enamels could melt at slightly different temperatures. Remember to experiment and record your results!
The enamels start to melt prior to the threshold temperature of 1400 degrees (instructions state 1400-1500 degrees) so holding at 1360 degrees for 15 minutes (or less) has been sufficient to thoroughly melt the enamels yet maintain the shape of the casting. But if are working with thinner glass that is going up in temperature much faster, it may take longer to melt the enamels.
You can also mix the enamels with a binder (Thompson's carries several types of oil, agar and an agent called Klyr-Fire) so you can apply them like a paint which works well for non flat surfaces. There are many colors available including ones that are very close in color to the fired greenish-blue color of recycled window glass. These enamels add a lot of shine to your glass work.
I will post a photo of the fired enamels next time.
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