Fusing glass, dealing with cracks...ARGH!!!

[molly]

Hi everyone. This is my first post here, and I am just learning how to fuse glass. I tried my first piece yesterday, and was so thrilled! As it melted, the colors blended beautifully! (kiln has no peep hole, so i opened the door just enough to peek in.....could this be a problem?) Unfortunately, it cracked as it was cooling. I decided to try again today, with the same results. I have an older, used kiln with no controller. It does tell you the temperature inside the kiln, but that's all. It also has some chips in the firebrick on the front door which might be letting air in, causing the kiln to cool too fast. (going to reapir that as soon as my kiln mortar arrives in the mail) The kiln also seems to heat up rather quickly....it goes to 1500 degrees F, in about 1/2 hour. It cools to 100 degrees F. or less in about he same amount of time. I know I need a controller, but I am unemployed right now, and have NO money....(the typical "starving artist")...any advice? How can I get the kiln to cool more slowly? Is this the problem at all? Is there any way I can insulate the outside of the kiln? I am VERY frustrated trying to figure all of this out. I cannot afford a new kiln, either, so need to find a way around this glass cracking problem if possible. Will I master this with experience? Or do I just have to wait til I can afford all the expensive equipment?? Thank you in advance for any advice. Molly.

[Tony Smith]

Molly,

You don't say how large the kiln is or if it has an infinite switch (numbers from 0 to 10 or low, med and hi settings). I've never seen a kiln with just an on-off switch, but I imagine they exist.

Something is definitely amiss if the kiln cools to 100 degrees in a half hour... with the kiln closed up, it should take two or three hours (for a small kiln) and several hours for a larger kiln.

The key here is that you want to slow your decent way down... this is accomplished in some kilns by turning the infintie switch to medium for some period, then to low, but you will have to spend a few afternoons to get to know your kiln and what temperatures you get with different settings.

Tony

[molly]

Thanks for the reply, Tony! Yes, the darned thing just has an "on" and "off" switch...no medium, lo, or high. Perhaps once the firebrick is repaired, it will cool more slowly? In the meantime, I guess I will just try and come up with some safe ways to insulate the gaps during cooldown. Any other ideas or suggestions are appreciated! Thanks so much....

[Tony Smith]

Molly,

Where are you located? If you can find a refractories dealer in your area, you could buy a yard of ceramic fiber blanket from them for probably under $10. You could use the blanket to stop up the holes and maybe even drape it over the kiln for the cooldown... look in the yellow pages under refractory. Email me offline and I'll send you some if you are in the US.

By the way, what kind of kiln is it and how big is the interior?

Tony

[Carol]

Thanks for the reply, Tony! Yes, the darned thing just has an "on" and "off" switch...no medium, lo, or high. Perhaps once the firebrick is repaired, it will cool more slowly? In the meantime, I guess I will just try and come up with some safe ways to insulate the gaps during cooldown. Any other ideas or suggestions are appreciated! Thanks so much....

Molly...does your kiln have more than one element? Some of the old American Beauties have 4 elements. If it has two or more you might be able to turn just one on.

The only other suggestion would be to get yourself a timer and turn the element on for 20 minutes, off for 20 minutes and keep setting the timer to go do that...but that's really the hard way to fire, somewhat analagous to pushing elephants uphill. (You might have to adjust the time to find the magic coolign rate).

The fire up and cool down temperatures seem really really fast for a large ceramics kiln.

[Jerry]

Had the same problem with an old ceramic kiln. It was made by "Gare" and was 23 inches across and 30" high. It had six sets of elements each having an on/off switch. I solved the heating problem by only turning on one element at a time until I was over 1100 degrees. Cooling was another issue. I found that by only having two elements on and the lid cracked to two inches, I could maintain an excellent annealing temperature.

All this is to let you know you aren't the first person to enter the world of kiln firing with a "less than desirable" kiln. Your problems can be beat but will take some ingenuity on your part.

Heating in any kiln as fast as you said yours heats is a problem. Sooner or later you WILL thermal shock the piece as it heats, so you have to figure out how to slow things down. Turning the power switch on and off at ten minute intervals is an option, not a good one, but it may be the only way.

What concerned me was how fast you said you cool. That's made to order for annealing fractures. You simply can't cool that fast without trouble. I doubt if the holes you described are the problem, unless they are the size of grapefruits.

How large is this kiln? How thick are the firebricks? Are there any other places where air might be leaking in? How long did you keep the door open when you "peeked?" And, how big are those holes?

Say some more and we will see if we can muddy your waters enough that you can figure it out.

Jerry

[molly]

No, it's a little baby...interior measuring about 3 1/2 inches deep. 4 1/2 inches high, and about 4 inches wide. It has two elements...one on each side. but no way to turn on just one element. There is a toggle switch on the front of the kiln...if it is UP, the kiln is on. If it is DOWN, the kiln is off. The only other thing it has is an external temperature gauge....but there is no way to REGULATE the temperature. I have been fusing my glass on a terra cotta tray, painted with kin wash. All goes well and it melts beautifully, but cracks later. If I have to "push an elephant uphill"....I just need to learn HOW to push the elephant. I don't mind doing things the hard way until I can afford to do better. Yes, I am in the U.S.....North Carolina to be exact. We are in a rural area where nothing "out of the ordinary" can be bought...we have to go out of town and/or order it. I thought of the fireblanket trick, too....maybe that is the thing to do. plus, patching up the large chips in the mortar should help too...some are large enough to peek into the side of the door, so I KNOW it is losing heat that way. It also heats up very fast...I suppose this is normal? This is my first kiln, and first attempts at using it, so I am a bit baffled sometimes. Thank you for all the help! Keep those answers coming! LOL!

[Jerry]

Okay, now we have some idea what you are dealing with. Get thee to a larger city and find a quality hardware shop. There you will be able to find a heavy duty dimmer switch or a thermostat for a stove or something along that line. You can install such a thing in in your power line to slow down the current flow. You will need to examine your kiln and fine the amperage to tell the salesman. These things are available and will help slow the thing down. Another solution is to use a heavy duty soldering iron controller, which is about the same thing. I've got a Paragon "Quick fire" connected to a Glasstar iron controller I've been running for a year using the controller to slow it down. Otherwise, it hits 2000 in 14 minutes! Works great.

Good luck,
Jerry

[molly]

Gosh Jerry! Thank you! That should save me a lot of money....great idea! And my fiance is VERY handy with things like that. I will show him your post tonight when he gets home from work. Once I install the dimmer or other controller, and patch up the firebrick, that should do it! YAY! I thought I was going to have to buy another kiln! (that I cannot afford). Thank you so much for hte handy, money saving advice...have a great day.....Molly.

[Tony Smith]

Jerry,

I never thought of a dimmer, but then my smallest kiln draws 13 Amps... how large a dimmer were you able to find? The largest dimmers that I've seen at a hardware store only go to 600 Watts (5 Amps).

Tony

[Jerry]

Of course that could be a problem. If you can't find one that will handle the current load you shouldn't do it. I found them at Home Depot in the electrical section. However, I've decided that my soldering iron controller does a much better job. Glasstar makes one that will handle the Quickfire very handily.

Jerry

[Jane Lindell]

Molly:

Jerry and Tony have given good advice on your kiln. Heating and cooling as fast as you are can definitely cause cracks.

One more idea though - just in case you don't know this. Are you using "compatible" glass? You need to make sure that all the pieces of glass you are fusing together have the same co-effiicient of expansion. If not - the glass will crack. Mixing ordinary stained glass without testing it first is a recipe for cracks.

Brad's tutorial has a wealth of information - here's the compatibility link from above:
http://www.warmglass.com/Glass_compatibility.htm

Sorry if you already know all this -

Jane

[charlie]

Molly,

Where are you located? If you can find a refractories dealer in your area, you could buy a yard of ceramic fiber blanket from them for probably under $10. You could use the blanket to stop up the holes and maybe even drape it over the kiln for the cooldown... look in the yellow pages under refractory. Email me offline and I'll send you some if you are in the US

bad idea. kiln outsides aren't designed to deal with higher temps. putting blanket over the outside could cause the outside to fail more quickly. it will definitely affect the life of the meter on the pyrometer if that's inside the blanket.

[molly]

Thanks for all the great advice. I am not sure if my glass is compatible, as I just began these projects 48 hours ago, and still have a TON to learn....I ASSUME they are compatible, as they are glass "blobs" in different colors, manufactured by the same company. They are the same size, just different colors. I am melting the glass in a terra cotta tray. I wonder if anyone knows how big a difference it will make once I get my firebrick repaired? It is cracked along the door, and you can even see inside the kiln if you peep in a the correct angle. This should make a big differennce in cooling time, right? Sorry for all the dumb questions, it's just taht I am so NEW at this, and I AM DETERMINED to figure it out and get it right. There is so much of my work which has taken me ages to figure out thru trial and error, and I have been pretty successful. I am just really stubborn, and I do NOT give up! LOL! Anyhow, and more info would be appreciated. I will try almost ANYTHING to make this work...

[Tony Smith]

Molly,

Where are you located? If you can find a refractories dealer in your area, you could buy a yard of ceramic fiber blanket from them for probably under $10. You could use the blanket to stop up the holes and maybe even drape it over the kiln for the cooldown... look in the yellow pages under refractory. Email me offline and I'll send you some if you are in the US

bad idea. kiln outsides aren't designed to deal with higher temps. putting blanket over the outside could cause the outside to fail more quickly. it will definitely affect the life of the meter on the pyrometer if that's inside the blanket.

Good point Charlie. I was thinking of the fiber blanket more to cover the area where the hole was in the door/cover as opposed to cover the entire kiln (pyrometer, switch, wires and all). If the heat is dumping that quickly, that area is already being affected by the high heat.

And Molly, never assume anything when fusing. If you are melting "blobs" of different colors, you cannot assume they are compatible just because you bought them all from the same manufacturer. Get some compatible glass, or at least cut some shapes out of the same sheet of glass and experiment that way. Otherwise you'll become frustrated very quickly.

Tony

[charlie]

Good point Charlie. I was thinking of the fiber blanket more to cover the area where the hole was in the door/cover as opposed to cover the entire kiln (pyrometer, switch, wires and all). If the heat is dumping that quickly, that area is already being affected by the high heat.

i'm on the paragon email list. about every week or two i get a tip from them. one of them was the fact that the outside skin of a kiln is not designed to be hotter than it already is from normal cooling. putting blanket on any parts of it may cause that part to be degraded, or even destroyed, over time, let alone be a fire hazard.

here's the entire tip for that week:
Some of these safety pointers came from experiences that I heard from kiln owners. Following these pointers adds very little extra time to a firing.

1) Do not leave the kiln unattended during firing. Check the kiln from time to time. Observe the normal sounds that it makes and length of firing time. Once you are familiar with the normal operation of your kiln, you will know when something goes wrong.

2) Keep the lid closed when the kiln is not in use. This keeps dust out of the kiln. Also, should someone turn on the kiln while you are away, the closed lid will keep the heat safely inside the firing chamber.

3) Never place anything on the kiln lid, even when the kiln is idle. If people become accustomed to placing papers and other objects on the kiln, they may forget and do that while the kiln is firing. During operation, the lid may get hot enough to burn combustible materials placed on top of it.

4) Remove all tripping hazards from around the kiln. Keep the kiln's supply cord out of traffic areas.

5) Do not let the cord touch the side of the kiln, which may damage the cord.

6) Avoid extension cords.

7) Do not remove the ware from the kiln until the kiln has cooled to room temperature. It is possible for thermal shock to break hot ceramic pieces. The sharp edges of broken ware can injure hands.

8 ) After firing glazed ware in your kiln, examine the shelves for glaze particles. Sharp slivers of glaze stuck to the shelf can cut hands. Before rubbing a hand over a shelf, be sure the shelf is free of glaze shards.

9) Fire only approved materials purchased from a knowledgeable supplier. Do not fire marbles, pieces of concrete, rocks, and other objects. Rapid heating to high temperature can cause violent reactions in many materials.

10) Greenware, which is unfired clay, must be bone dry before firing. Moist greenware can explode inside the kiln, damaging the ware and the kiln. Place a piece of greenware against the inside of your wrist. If it feels cool, it is too wet to fire.

11) Do not fire cracked shelves. They can break during firing, damaging the ware inside the kiln.

12) Store kiln shelves in a dry area. Moist shelves can explode inside a kiln.

13) If you smell burning plastic, turn the kiln off. Examine the wall outlet and supply cord for signs of burning.

14) Never place extra insulation around the kiln in an attempt to conserve energy. The extra insulation can cause the wiring and the steel case to over-heat.

15) Do not wear loose-fitting clothing around a hot kiln.


the email tip is mostly for ceramic kilns, but sometimes they're topical for glass kilns too. sign up at http://www.paragonweb.com/news.cfm?type=subscribe

[molly]

i guess all i can do is keep trying then, huh? the piece i melted this morning was 3 colors. two came out beautifully....one is all cracked. guess i will break it up and put it into my tumbler. I told myself when I began this new venture, that if the glass cracked, I did not care...i would just tumble it until it was man made "sea glass", and use it that way. BUT I CAN'T "SETTLE" for that! It just drives me nuts when I cannot figure something out. I guess I will just continue experimenting. Is there any way I could enclose the galss in a small cea ramic box or something, and THEN fire it in the kiln? Or would it not get hot enough. Just tossing around "green newbie" ideas here. Again, how much do you think it will help once the kilns firebricks are repaired? That should get done by next week this time.
Thanks again for all the help......Molly.

[bivbeadies]

Hi Molly,

I read through the posts and agree with the commentary on the kiln issues...you need something set up where you can control the heat better than an on/off switch...it's a very small kiln, from the sounds of it...

But the cracking glass is another story...especially with mystery blobs of glass that you are not sure are compatible or not...best bet is to fuse with glass that is tested compatible...Bullseye is excellent for this...as is Uroboros...and Moretti even...general stained glass pieces are risky because most of them are not tested compatible...when you say 'blobs' and that they are made by the same mfg., are you referring to those little glass marble type 'blobs' that they use in flower vases and fish tanks? What type of glass is it? I guess until you know if they are all tested compatible, you may continue to have trouble with cracks...but the tumbled sea glass idea sounds pretty neat!

Working with different glasses to make beads, I've found that glass that's allegedly in the same COE range don't always work nicely with each other...like Lauscha and Moretti...sometimes they just don't work with each other even though they are 'supposed' to be compatible - when I heavy encase with the L clear over M black (and especially when I use silver leaf or foil!), I always get cracks...and even in the Moretti line...the opalino glass doesn't always behave with the other glass it's supposed to be compatible with. Same with Bullseye - you can't mix and match the sheet glass willy nilly - it has to be from the tested compatible line. Sometimes it's experimentation and practice.

You'll get a hang of it!! Keep us posted!!

[molly]

Thanks for the info and ideas...I STILL want to know if any of you think things will get better once the kiln 's firebrick is repaired around the door. Yes, it is a very small kiln, and I WISH I had the money to buy another one, but I just don't. The tumbled sea glass is coming along nicely, and it IS a sort of "tye dye" looking glass I am happy with...BUT I WANT to learn to do regular fused galss, and at least have an Occasional success! LOL! As far as glass compatibility, how can u tell waht is compatible and what is not? So I COULD just melt down a few shard from the same broken bottle, right? I was hoping not to have to buy glass just to fuse it. I was hoping to be able to "recycle" wine bottles, beer bottles, etc. Yes, I am cheap, but the older I get, the more often I refer to it as being "resourceful". I make all kinds of jewelry, and specialize in wrapped glass....especially sea glass. I'd love to be able to fuse some pieces myself, and wrap them in sterling and gold. I think they would be lovely. But I have to get these cracks to stop first! One other question....at what temperature does annealing take place? How long should I soak at the annealing temperature? Thanks again for all the help.

[Tom White]

Anealing is not a temperature or holding the glass at a temperature for a given time. Instead, anealing is the gradual cooling of the glass to relieve the stresses in it which have been caused by heating and moving the glass in the kiln. The "anealing temperature" ( 1000* F. for float glass, 960* F. for Bullseye, etc.) is a starting point for the anealing process. The soak time at that temperature is used to allow the glass to reach that temperature throughout the whole mass of the glass. The gradual (less than 100* F. per hour) cooling of the glass to about 700* F. is the actual anealing process. The typical anealing cycle most often published is for 1/4" thick glass. Thicker glass requires slower cooling cycles to avoid trapping stress in the glass.

Repairing the bricks in your kiln will help provide more control over rate of temperature change of your kiln but until you have some means of slowing the rate of change, especially on the cooling cycle, you cannot expect consistant good results firing glass.

Best wishes,
Tom in Texas