Jodi McRaney RushoAnd we’re back with more questions from readers for Q & A Monday. Today’s questions are all about working with crushed recycled glass, or frit. I’ve left out the personal details for privacy, so if one of these questions is yours and you’d like attribution and a back link, please let me know. If you have a burning (melting?) glass question, send it on over. I may even have an answer for you.

  • Q:  I have a kiln that I have been playing and experimenting with for months now.  I adore wine bottle glass, and have had complications casting melted wine bottle frit that I make.  From research I have done, and some of my experimenting, I have found that wine bottle glass is difficult to cast unless fired at very high temps.  Even then, I have had to do a lot of cold working with the pieces I have tried to make after firing.  I love to try and make little jewelry pieces out of the frit.  Do you have any suggestions for working with wine bottle frit, including firing schedules at all?  Thank you so much!
  • A:  Frit is a little complicated.  The smaller the pieces, the more heat is required, so yes, they do require high temperatures.  Then, add in small jewelry molds, which are a small volume of glass and it gets even more tricky.That being said, the easiest thing is to use small ~1/4″ frit pieces and try this firing schedule:300/hr to 1100 hold 10 (this stop makes sure your mold and glass are all the same temperature)
    300/hr to 1650 hold 20
    9999 to 1020 hold 10 (annealing stop)
    200/hr to 750 then offThe annealing is probably conservative, and with jewelry pieces, a natural cooling cycle is probably annealing enough, but I’m kinda careful about that stuff.  This is the schedule I use when I’m making panels with wine bottle frit, or using jewelry molds.  I do still have to cold work, but I usually do that on a tile saw or grinder and then fire polish the pieces.

    What we are doing here is heating the frit chunks slowly enough and holding at a temperature where they will melt, but not so high that they devitrification process is accelerated.

    If you are using smaller (like sugar) frit, then the process is more similar to pate de verre.

    I will try and do some more conclusive testing myself, particularly as this is a question I’ve also been working on for a long time, it would be good to get it nailed down.

  • Q:  I love your site and your work. I’ve been fusing recycled glass for a few years now (mostly just slumped bottles) and have been having problems getting bottle “frit” to full fuse in a mold. I’ve used your firing schedule most recently and the pieces are still not smooth and shiny. Most still have a pebble texture. Should I raise the target temp or hold the ramp longer?
  • A:  Yes, you’ll have to raise the target temp and increase the hold. I’ve had good luck with 1750-1825 range, depending on the frit size.  Hold for 10-12 minutes.  Since the jewelry pieces are small, you can decrease the annealing time if you wish.
  • Q:  Hi Jodi.  I recently bought new running pliers, same art kind and they were good until the silicone or rubber or whatever that covers the ends started breaking down. Now they break off a bit under on one side.  But the question I have is about Fusing temps.  I have been trying to fully fuse broken bits of the same bottle so that the glass flows to an even surface.   I  have something in the kiln right now,  2nd try that is set for 1625 F for 10 minutes.  Last try was 1600 for 5 minutes. I have been using a Fast program to find out the top temp,  but have recently read that air pockets insulate and thats why you need a slow Ramp?  would this help?  For this experiment I used three sizes of the glass, laying out the biggest ones first then the med. then the smallest.   Can you actually get it to flatten out?  Oh I am putting the glass on fire paper with a 6×6 square fiber board frame around it.
  • There are a couple of things I would try here.  The ramp speed is probably contributing.  Not necessarily because of air pockets, but because you are speeding right through the transition zone which means the glass doesn’t have a chance to equalize out in temperature.  That means the outside of the glass will crystallize before the inside of the glass melts.You don’t mention how fast the ‘fast’ ramp is, ideally, I like to go around 300/hr, although you can go as fast as 500/hr with good results.I think your top temperature is too high for the broken pieces of glass.  The smaller the pieces, the more heat it takes to fuse them, but what your doing won’t take that much heat.I would go to 1550 or 1575 and hold for 15 minutes.

    Also, keep in mind, some bottles just won’t melt smoothly into a sheet.  I typically have trouble with the celery green ones and some clear ones.  Darker colors melt more smoothly. If you’d like to send me a photo, I may have other suggestions.  I too had running pliers that the rubber came off.  Hate that!  I ‘fixed’ it by taping on rubber drawer liner, but it wasn’t a great permanent solution.  I’ve wondered about the rubber tool dip that you can use for plier handles.