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Since 1966 I have been doing glassblowing and making ornamental specialty items. My type of glassblowing is called "Lampworking." The other kind is called "Off Hand" and is where you take raw glass from a furnace. I use rods and tubes to create what I need. I hope you will consider purchasing some of these items as it also helps support this website!


I am no expert on anything having to do with glassblowing or lampworking, but have learned a few of the simple things. I looked for many answers on the internet and only found a few vague (to me) references having to do with many things...especially annealing glass.

Usually even the rawest beginner knows that glass that is uneven in temperature will crack and glass that has been heated in a particular area and then not cooled properly, is in serious jeopardy of cracking. Let it cool and then go back and re-heat it and it will probably crack. So the way to solve these problems is to get an annealing oven (or kiln or lehr).

I have had an annealing oven for about 35 years, my former one being an analog version. At first I had an analog pyrometer (the thingy that tells you the temperature), but soon enough got a digital one. You can still buy them on the internet.

Finally I got a digital annealing oven. I have a Paragon (see: www.ParagonWeb.com) F130. My former one was a Paragon and I have found these people to make the finest quality you will ever see and have the best support you will ever find! Love them to pieces! For my purposes (and budget) the F130 is all I currently need. You can program it, stick your beautiful creation into it, punch it on and go to bed and get it out in the morning.

So..............after all of that jabber, here are a few hints on how to properly anneal your glass. Excuse me, but I only use Corning 7740 Pyrex® because I am pretty lazy and it works very well. Soft glass (COE 103) will crack more easily than the "borosilicates" (COE 33). These suggestions are if you are annealing a piece that is already at room temperature. If the piece is really hot, then pre-heat the oven to at least 950 and start, but the piece has to be uniformly hot or you might crack it. The same thing works in reverse. If you are going to seal something to a piece you are working on, it is good if you have already pre-heated it at about 1040 degrees F so that it will already be hot when you take it out of the oven. Make sure that the piece you are working on is really hot when you seal it on.

FIRST: The rule of thumb is that for every quarter inch of thickness, you need to anneal the piece for an hour. (Some people might say 30 minutes, but I am conservative.) There is a lot of latitude in small pieces, for many small pieces don't have enough stress in them to even need annealing, but it would always be more beneficial.

SECOND: The "STRAIN" point of Pyrex® is 950F whereas for the other borosilicates it is 960F. So spend your life's savings on a good oven like mine and program it to go up to about 970F for the first ramp. And set it to FULL BLAST if your piece is "robust" and is not likely to shock and you're starting out a room temperature. Why? Because we need to get there in a hurry so that the glass is now "safe" from any cracking. (If your work is already HOT, then have the oven already warmed up.) But why the 970F? Because the controller is not accurate enough, nor the firebricks thoroughly hot enough to properly hold a high temperature yet—and when it gets to that temperature, you're naturally going to have the controller hold it there for about 10 minutes, so that all of the glass can become the same temperature (at the strain point)...AND...when it starts "soaking," the temperature will drop as much as 18 degrees or so. But since the strain point is 950, we don't really care. It will still be safe. IF...you've already made an object, and it is quite hot, then try your best to get the entire piece about the same temperature throughout and then pop it into the oven at about 950F because we don't want to cool it down if it is already hot.

THIRD: For your next "ramp" you are going to want to go all of the way to the proper target temperature for annealing. For my Pyrex® it is 1040F. Now here's where it gets a little tricky. You may have thin glass on your piece and you don't want it to SLUMP and thereby become distorted, so since Pyrex® starts slumping at about 1050F, then stay away from there. Here's how you can easily do it.

FOURTH: This time when we raise the temperature from our previous 970F to 1040F we lower the speed by which it achieves that temperature (ramp speed) to about 140, which means that it raises the temperature 140F per hour. In other words...SLOWLY. You can go as high as 200. By letting it ramp up slowly, then you let the firebricks get a uniform temperature throughout and the whole oven will achieve uniformity. You will want to set your "soak" period to at least an hour or more. I just made a dolphin that was an inch and a half thick, so I set it for 6 hours. Holy Cow! That seems like a long time, but failure is much more lasting! If you gaze at the temperature like I sometimes do, then you will find that the temperature will probably only rise to about 1043F at most, which is still SEVEN DEGREES below the slumping point. Gradually the temperature will go back down to 1040F or even a little lower, but soon it will become very steady at almost exactly 1040F. For the full "soak" time.

FIFTH: Now we have annealed our piece and want it to all cool down. BE PATIENT!!! The more slowly you cool it all down, then the less stress there will be in the glass (cannot be overemphasized!!!). Do something else for awhile. But program your controller for a series of steps (in temperature) DOWN from 1040F. Use a slow speed like about 200-300 so that the oven won't cool down quickly, for the "slower the better." Go down to about 1020F and hold for about 20-30 minutes. Then go down to your 970F again and hold for about another twenty minutes. Keep the speed SLOW! Then go down to about 920F. Hold for about 15 minutes. By holding, the oven is forced to really slow down. Now we are BELOW the strain point, so stress might be induced, so we are going to go slowly. Then go down to about 800F and have a speed of about 200. Hold for about 20 minutes. Then go down to about 600F and hold for about 10 minutes. After that, you are safe. Pyrex® has a shock point of about 350F, which means that if it is cooled about 350F really quickly, you could be in trouble. But your room has a temperature of probably at least 70F, so if your oven is at 400F, then even if you took the piece out, it would probably be safe. Don't do this. Leave it in the oven. But the point is, that your annealing cycle should be OVER. Wait until it has cooled down to within 50F of room temperature if you have to, but I prefer to let it cool all of the way down to room temperature, so that I can open the door and simply pick it up with my hand. You know...the hand with all of the burn scars. But seriously, the more patient you are, the better it will go. Many artists cool as long as they anneal, so get it in your head that you're not in any hurry if you want genuine success.

One of the nice things about properly annealing your glass piece is that after it is completely cool, if you made any mistakes in creating it, you can usually (if you're careful and warm the area slowly!) fix the mistake. Bad joints can be more properly sealed by using a tiny pinpoint flame for a full, proper seal. If a seal has visible strain marks or is cloudy, it is a bad seal. If you boiled the glass and have too many bubbles in it, it is also a bad joint. A "cloudy" joint is a bad joint. If you can see where the glass is joined to the other piece of glass, then it is a bad joint. A good joint just flowsinto the other piece of glass. Experienced people will pull off a bad piece like that with a pair of tweezers. Naturally, after repairing (especially for a crack), then you have to run it through the firing cycle all over again, but that's the price of excellence.

I'm sure some of you experts have differing ideas on this, but I was just vain enough to want to put something on the internet about this subject because I was so frustrated by not being able to find out the proper information on my own. I had to do it "trial-and-error" which is the surest method, but also the slowest. If you have better suggestions, then send them to me and you can "school" me and I will thank you.

The "SOFT" glasses will have a much lower set of temperatures, but since I don't use them, then you will have to look them up yourself.

REMEMBER: Annealing is about 70% science and 80% ART! The best of Blessings to you. If you're in a hurry to get your glassware out of the oven, you might consider another hobby. Success is much more sweet than failure. Also, if you have to make any last minute adjustments, like repairing a sudden crack, it will be easier to do with a very small flame and your work already annealed.

Last suggestion: Don't drop it when you take it out of the oven. I've done that! Other suggestion, (to me especially) put the hot end of the glass away from you and quit forgetting which tool you have just used in the flame and don't pick it up or touch the hot part. When you burn yourself, get it cold quickly and for the next week, run cold water over the wound for about 5 minutes at least 6 times a day. I was a hospital corpsman in the Navy and know that you can cure nearly any wound if you can just keep it REALLY CLEAN. This doesn't mean you can put the standard ointments and dressings on it, but at least 6 times a day, let clean cold water just flow over it to clean the wound. Now that you're really depressed you can get back to your glassblowing shop.

As Harry Truman said, "If you can't stand the heat, then get out of the kitchen."

Mike says, "The chances of you getting burned in glassblowing are 100%, so organize your tools, think a little and minimize your risks. Then write me and complain that I didn't warn you enough. Then also write me and tell me of your successes. I had no teachers, so if a knucklehead like me can do it, then so can you.














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