Here are a few of the questions that were sent my way last week, the answers may help others as well, so I’m posting them here. If you have a question, don’t be shy, send it on over! (I have left off the names of the question senders for privacy. If you sent a question and would like attribution and a back link, let me know! J)
Question: I have a ceramics kiln that will follow your schedules but I am scared to use glass in it for fear of wrecking the kiln itself. I’ll stick to simple fusing and melting for now until I get used to the process- as opposed to pot melting and molding. So my questions are: Are you using a glazed bowl for slumping prepared with kiln wash inside and out or do you use unglazed bisqueware with kiln wash? What is the chemical you spray on glass to keep it from going cloudy? We are in New Zealand so chemicals, not brand names are more useful. Will slumping a wine bottle or even fusing it ever make the bottle liquefy so much as to run off the edges of the kiln shelf- assume I put it at least three inches from the edge. How thick does the kiln wash need to be?
Answer: First, let’s talk about wrecking kilns. It’s actually pretty darn hard to do. Really, the only way to wreck a kiln is to melt glass into the elements or into the firebrick itself. There are some pretty basic things that we can do to prevent this. First, kilnwash the floor of your kiln. Do several nice thick coats. Then, if glass melts off your shelf, it won’t ruin your kiln. If you are casting, you can always put your mold or dams inside a plant saucer or other terra cotta container. This will contain your melted glass in case of mold failure or cracking.
Okay, now, about molds. Yes, you can use a glazed bowl as a mold, IF you sandblast off the top layer of the glaze and kiln wash it. I have had very good luck with re-using bowls I find at thrift stores and yard sales. Make sure the glass is blasted off the inside (the back doesn’t matter) and kiln wash the inside. You can also use bisqueware. In fact, that’s exactly what most glass molds are. You can also make your own ceramic molds and bisque fire them. Just remember, all molds have to have a separator on them, either kiln wash or spray on.
I don’t spray any chemicals on my glass. Clean the glass very, very well using a white vinegar and water solution and fire away. The manufacturing process of your glass will have much more to do with devitrification than anything else.
Fusing and/or slumping a bottle will not make the glass liquid enough to run off the shelf if your thermocouple and controller are working correctly. Slumping will cause the glass to heat enough to bend and fire polish, but not enough to lose details or to become liquid. Fusing will cause the glass to become soft like taffy, or thick honey, which will cause the glass to flow until it reaches an even 1/4″ thick.
It is important to make sure you leave enough room for the bottle to flatten, here’s a quick way to tell how big the bottle will be when fused flat. Kiln wash should be 3-5 coats thick, based on manufacturers recommendations. Typically the label will tell you the mixing instructions for that particular brand.
Question: I know your schedule must be packed, but I would greatly welcome your recommendations on a kiln. I was also wondering what it costs (energy wise) to fire some of your more basic projects; a guestimate or ball park. I know I am asking a very open ended question which has so many variables, but using one of your tutorial projects for instance might give me a rough idea of energy costs.
Answer: If you are intent on working in recycled glass, I would recommend a ceramic kiln with a digital controller. It doesn’t have to be a giant one, something with a 14″ shelf will hold you for a good long time. It’s often possible to find used ceramic kilns where used glass kiln are very scarce.
That said, if you plan to do this as a full time job, you will really want to think about a bigger kiln at some point. Unless you already have a large business built up, you can still start with a medium size kiln and work up. I used my smaller kiln for about 7 years before I upgraded.
The temperature range you need is up to 1875 F. Most ceramic kilns go to 2250, so you should be fine there. I own a Skutt 818, which is an 8 sided kiln with an 18″ diameter, 23″ deep. I used this kiln for about 7 years, including the years I did the Art Market every weekend. (our Art Market is part of our Farmer’s Mkt). It has 3″ thick fire brick and a super easy digital controller.
My glass kiln is a Denver glass kiln, the 30″ x 60″ x 12″ deep. Fiber lined with a fire brick bottom. It tops out at 1650, so it’s good for fusing and slumping, but not casting. The controller is AWFUL! But, I hear the controllers have gotten better since then.
So, firing costs:
For a full fuse, the Denver runs about $2.50 at .12c/kwh. For a slump, it’s about $1.80, that’s using my standard firing schedules. Remember how big this kiln is too, if I’m fusing plates, I’ll do 12-15 at a time. Same for slumping.
The Skutt is slightly more expensive, despite being smaller. I think that the firebrick doesn’t insulate as well as the fiber insulation. So, a fuse would be about $3, a slump around $2.25 and a casting (all the way to 1850) is about $5.00.
Question: Is it possible to use picture glass instead of window?
Answer: Yes it is. The glass is significantly thinner, but should behave the same way.
Answer: Here’s where it gets sticky. I don’t have any way of knowing what process was used to ‘non-glare’ the glass. There are several. If the glass is coated with a polymer type coating, the fumes can be very, very toxic.
If it was etched with acid or something like that, it will work fine. You could try scratching on the non-glare side with a razor to see if anything peels off.
Answer: I would hold the pieces flat and loot at the reflection of a light bulb. The reflection should be much more clear on the ‘glare’ side. Or fuzzier on the non-glare side. The tin side is a different thing, but I have never bothered about it, doesn’t seem to make any difference if you fire tin side up or down.
Answer: I wouldn’t think it would matter. You may have better results with the non-glare sides facing each other, particularly if the non-glare is a coating. You may get some surprising effects, which would be awesome.
Question: Your window glass firing schedules are rather timely. Must I use these same schedules if fusing non-glare picture glass?
Answer: Certainly, although you may want to decrease the top hold time because your glass is thin.
Question: Does devitrification happen more frequently with window or clear glass? I was told by a fuser whom does wine bottle projects that greens and blues are less likely to turn milky than clear colors.
Answer: Darker colors do fuse more smoothly than clear bottles. The manufacturing method of the glass seems to have a larger effect on devitrification than the color. Float glass that was manufactured recently is quite easy to fuse with. The Float glass industry is so huge at this point, they have glass making down to a fine science. Older plate glass and even older float glass is quirky. Anything made in the last 25 years will be pretty predictable.
Chances are your non-glare glass is less than a year old, so I would think it will be fine.
Question: 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. Looking forward to your response,
Answer: 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. My suspicion is that you are actually overheating the glass and speeding up the devitrification process.
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.
Question: In your past emails you talked about using embossing glue stamp pad to rubber stamp glue then sprinkle with frit. I got a couple of different stamp pads and tried this. The glue didn’t hold enough frit to show up very much. I did cap it with glass. What kind (brand) of pad did you use or any other advice.
Answer: I’ve attached a photo of the embossing pad and ink that I use. I tried a number of them as well, this was my favorite. Also, make sure you use the frit that is the size of granulated sugar, the powder doesn’t stick down enough volume to give you a good color.
I have experimented with using the larger frit size, tipping it off, and then using powder, that gives a nice coverage, but is kind of a pain.