Magic Kiln Tactics
By Brian Kerkvliet, Copyright 1995
In my last issue I mentioned that I was going to evaluate the types of kilns that are out there for bead workers to use. In addition to the basic issues that I covered in my first column, on kilns, annealing and reducing the health risks that vermiculite pose to the bead maker, I would like to expand on the avenues that kilns open up for lamp workers.
Pick up pieces
Have you ever tried to make a piece that has a lot of surface relief detail, but by the time you finish the last detail the bead cracks because it got too cold? Then you look at the clock and you realize that you just wasted 1 hour and 30 minutes on that piece! Then you think to your self there must be a better way! Well I'm here to inform you that there is! The basic idea here is to spend time making your detailed parts and then put them into the kiln to be attached later. This allows you to spend quality time on the decorative portions of your piece without having to worry if you are keeping the whole piece hot. It will also give you a break halfway through, allowing you to recollect you creative thoughts. Or go to the bathroom!
When using a kiln to pick up parts, it is desirable to have a kiln that is both fast in heat recovery and easy to get in and out of without any hassle. After the kiln is up to annealing temperature, make the parts that you'll attach later to the finished piece. Place these parts into the kiln so that they are positioned for easy access when you want to get them out. These parts can be as simple as a single petal of a flower, to a whole blossom, or possibly a critter of some kind like a turtle. After the parts are put into the annealer, take a break and think about how they will fit onto the finished piece. I find that making a sketch of the piece helps in the process. Then sit down at your torch and make the base armature that you will attach the parts onto. Keep in mind size and proportion. It is easy to make parts that look small enough until you put them onto the piece, at which time you realize that they have grown in the kiln! So remember to think of scale!
Once the armature is completed, get it all nice and warm in the back burner and simultaneously heat up the tip of a clear rod to use as a punty to pick up the part out of the kiln. Attach the punty to a part where it will be easy to remove later. I use a glass punty because it is less apt to thermo-shock the part and you have a lot more control with a punty then you do with tweezers. Once you have the part puntied up, heat it in the inner part of the flame for a short time, then heat the base piece in the inner flame. Alternate these two pieces in the hot part of the flame and the back burner while you look and decide exactly where the two will be joined. Once you have determined this, heat up both attaching points so that they glow nice and orange. Then take them both out of the flame an position the tip of the part onto the base first and gradually roll the base so that the total contact points are connected. Push it softly together and then right before the glass sets up, pull the part away just enough to give it a nice gusseted joint. You want to be sure that there are no undercuts in the union otherwise you will have a weak spot. See illustration 1
If you are putting more then one part onto the piece it is advisable to attach the largest of your parts first and then work towards the smaller ones. This way you are less likely to melt and distort the first parts that you put on. After you have everything attached where you want it, get the whole piece heated up as uniformly as possible while trying not to melt the delicate parts. This easier to do using a smaller flame to dodge around the portions of the piece that are more apt to melt. When you feel that the piece is a nice even temperature place it in the kiln for its final annealing.
I know that this sounds a little like faith healing, but it really can be done! Sometimes it probably isn't the best use of your time. For instance, why heal little spacer beads when you can make a new one just as fast? However, you don't have anything to loose by investing a little more time into fixing a crack or chip on a piece that you have already put a lot of time into.
If you notice that a nice bead is cracked, don't touch the crack or expose it to much dust. This is especially true if the piece is clear or a transparent color. The reason for this is that oils from your fingers and small dust particles can get into the crack, and when its is melted together, you will be able to see this line of scudge. I have healed beads that have been broken for several years with good results. Before heating them up I put them in an ultrasonic cleaner with a supper clean bath to try to clean within the cracks.
There are several categories of cracks. Fractures or checks leave the bead in one piece but you can see the crack. These tend to be the easiest to fix, especially if you notice them before you take the bead off the mandrel. Broken beads are basically just that, beads that have physically broken into two or more parts, bummer! I think that it's always the best one too! These are harder to "heal" and obviously the more pieces the harder it is to put them together again. Humpy Dumpty never had it so good! Then there are chipped beads. Chips happen most frequently right around the mandrel hole. Usually this is the result of a slightly bent wire or barb on the end of the mandrel. File those ends! These type of repairs are relatively simple to do.
The best kiln to use for healing beads is one that allows you easy access to the work after it is up to temperature. Front loading is better for this application.
Ok , so you're ready to play GOD and heal some beads. Put the beads into the kiln so that you can easily get them. I prefer to have them situated so that one of the holes is facing the door of the kiln, for reasons described later. If the bead has broken into pieces try to clean the pieces as best as possible and dry them off. Then put the pieces together without touching the joining faces. Place these into the kiln so that they stay together. You may have to prop them up with some fiber blanket or small brick pieces to keep them from rolling around. If you have beads that are still on the mandrel place them in the kiln in such a way that the mandrel pokes out of the kiln far enough for you to get a hold of it without burning yourself. It is simpler if you heal checked beads or beads on the mandrel the first time through. After you get the hang of it will be easier to deal with the beads broken in pieces.
Once you have them all in the kiln bring the kiln up to annealing temperature. This needs to be done slowly so that you don't thermo-shock the beads. (annealing statistics) Once the beads are up to temp. You want to let them soak there for 15 to 20 minutes so that they are good and hot, then turn the kilns set point up to 970ûF for another 5-10 minutes. When it reaches that temp. Choose a piece of clear glass rod, heat the end and marver it into a point. This will be your punty, used to attach to the hot bead. Let the point cool down slightly then heat just the very tip of the punty. Take the hot punty and as fast as you can open the kiln and attach the tip of the clear glass rod to one of the beads. I prefer to attach this punty to the end of the bead where the hole is. This allows me to rotate it as if it was on a mandrel. The punty won't make as strong a joint there so it will be easier to break it off back into the kiln. When you first punty the bead up it will be very floppy and will feel like it's going to fall off. Well it might! Just be patient, if possible, close the lid to the kiln as much as you can, as you keep the bead turning inside the kiln it will begin to set up. This allows the hot part of the punty and the bead to equal out in temperature. After about 20 seconds open the kiln door up and go directly to the torch do not pass go and do not collect $200. Hopefully at this point your bead is still in one piece and on the punty. Heat the bead slowly at first with a softer bushy flame, then turn up the torch and bring the bead closer into the flame. You should now be able to see where the crack is. Ideally you want to heat the crack from one end to the other. By doing this you can work the air that is trapped in the crack out through the open end, making it vary hard to tell where the crack had been. As you are doing this don't forget to keep the rest of the bead and punty hot as well. At this point you should turn the kiln back down to 930ûF so that the other beads don't melt down. After you have sufficiently heated the crack so that you can no longer see it, it's time to transfer the bead off the punty and into the kiln. I use a tungsten pick which I slightly heat up so that it won't thermo-shock the bead. Insert it into the open end of the bead. Then give a sharp tap to the punty end to knock it off the bead. If a tap doesn't get it off, burn it off and remove any excess glass with the tweezers. If the hole isn't open it may be opened up with the tungsten pick. You want to be sure to keep the bead hot but not melted this whole time. Once the punty scar is fire polished, place the bead back into the kiln for the final annealing. If you find that using the tungsten pick is too difficult you can also use a pair of tweezers to grab the bead while you fire polish the punty mark. You do however need to preheat the tweezers so that they don't thermo-shock the bead and at the same time be careful that the bead isn't so hot that the tweezers make an impression. Like most things that you can do in the torch it may take a little practice, but the rewards are worth it.
When getting a bead out of the kiln that has cracked completely in two, stick it with the punty so that you touch the seam between both pieces. They may move around a bit but at least you have the registration in one spot lined up. Once you are in the torch you can position the parts properly using the tweezers. (don't forget to preheat them!) Then start fusing the parts together working gradually from one side to the other. The rest is pretty much the same as I described earlier. Fuse it together and if necessary tease the separate parts of the bead together along the crack line using the tungsten pick. Sometimes you need to heat the whole thing up fairly hot and marver it to sufficiently work the crack back together. Once it is fused together crack off the punty and fire polish the punty mark as described earlier. So now you can dig through all those jars of broken beads and go to town playing GOD! Or GODDESS as the case may be!
The Art of Annealing
This Topic seems to come up again and again. It is one of those mystical things that is difficult to see and understand but it's so important if you want your precious beads to out last you! There are many different sources of information on how to anneal glass. I have referenced some at the end of the article. Many of them are rather technical and can make your head spin and your eyes go fuzzy after a few minutes of reading them. What I shall attempt to do is take the mystique out of annealing beads, because it really isn't that difficult. I will assume that you have already read my column in the Sep./ Oct. Glass Art issue that describes the basic physical properties of annealing. What I will go over is the practical basics of annealing smaller beads.
The annealing table that is shown should be self explanatory with T1 -T6 being the various segments of the annealing cycle (ill. 2) . If you are starting the day out with nothing in the kiln then you can take the kiln up to annealing temperature (T3) as fast as the kiln will go. Then after you put the last bead of the day into the kiln follow table 2 starting with the anneal soak segment, T3. You want to figure what profile to use based on the largest piece that is in the kiln. If you want to anneal beads that you have had around for a while, or are heating up parts from room temperature start from T1 on the graph. Segment T2 has a faster heat rate that you can take advantage of if you are bring up to temp. larger pieces. This is because after the glass passes through the strain point it is lass apt to crack on its way up to annealing temp. For most practical purposes with beads you can join segment T1 and T2 into one slow ramp. You may take these up to annealing temp and hold them there all day if you want with no ill effects, so long as you bring everything down through the annealing stages T3-T6 at the end of the day. Annealing occurs in the segments T3- T5, so these are the stages to watch carefully. If there is any stress remaining in your pieces after segment T5 then it will be trapped in the piece forever, or until it breaks!
Many kilns have only an infinite switch and pyrometer for control of the firing cycle. This means that you will have to sit and watch the kiln until it gets through the T5 segment. At which time you can turn off the kiln and allow it to coast down to room temperature on its own. Different Kilns have different cooling rates and you will need to do some timing tests to determine yours. Basically the cooling rate depends on the amount of mass that has retained heat. Typically a kiln that is built out of brick will hold heat longer then one built out of fiber. However there are other things to consider such as the insulation value of the kiln, or how many pieces are in the kiln which add mass.
There are very few kilns that I know of that you can just turn them off after the annealing soak is finished. It is usually always necessary to ramp them down from T3 through T5 before turning it off.
In my search for bead kilns and controllers to review for this article I found that there were very few perfect controllers out there for the bead hobbyist to use. However I did find that several companies are working on producing a simple ramp and soak controller that will be affordable to use with the bead kilns listed in my review. To the best of my knowledge there is only one controller available, that's a low cost, plug and go type controller. Most of the other set point controllers that are available require wiring up in a electrical box with a relay, fuse etc. This can be rather intimidating if all you want to do is make beads not learn to be an electrician. However if you are inclined, or have a friend that is knowledgeable in such things you can get a single set point controller for between $125 to $180. Then you need to mount it into a housing and buy a relay. This will add another $50 to $75 depending on where you source them. If you choose not to go through the hassle of getting all the parts together for this type of control device all is not lost. Arrow Springs, Fusion Products and Frantz Beads are all working on a simple low cost controller that will be perfect for the lampworkers kiln. One model will be a set point controller with a percentage of power switch. Another model will allow you to have several ramp and soak segments per firing. If you plan on doing a lot more with your kiln that annealing beads than you may want to look at controllers in the $400-$800 range. You will find that in that range there are more to choose from and they offer you a lot more options in the firing cycle.
Now that you understand how to keep your beads from cracking, new ways of decorating in relief, make the kiln fire on a controller, when are you going to find the time to take me on a vacation! That's what I want to know!!
Bead Happy !
Set point controller This is a controller that is like the thermostat in your house. Put the temperature indicator where you want it to be and it holds that temp.
Plug and go: Plug the kiln into the controller and plug the kiln into the wall and your ready to go!
Punty: Traditionally an iron rod with a bit of glass on the end used for attaching onto other pieces of glass. In flameworking you mainly just use a piece of glass rod with a hot end.
Other information sources on annealing:
See Kiln Firing procedures and annealing: by Dan Fenton in Glass Art
Part 1 Nov./ Dec. '94 and part 2 Jan /Feb.'95
"Bead Basics" by Brian Kerkvliet ,Glass Art Sep./Oct.94 for other heat up and annealing requirements.
Contemporary Lampworking: A Practical Guide to Shaping Glass in the Flame , This book by Bandhu Dunham is tailored for the lampworker so it spells these techniques out in simple terms, as well as giving ample scientific formula to appease the tech heads. It also covers many other details on shop set up and safety, current suppliers lists, as well as mixing your own color in borosilicate glass . The best book on the subject, a must for any glass workers library.
Kilns and Controllers: