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Tips and Tricks
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Q:: I love the look of Raku. How do I get Reduction Frit to work? A:: Use reduction frits to create a metallic luster similar to a raku like effect. To use, place frit on a marvering pad. Heat glass enough to pick up the frit and melt it fully into the surface of the glass for best compatibility. Form to its final shape. Allow the glass to stiffen, but still remain hot. Then, quickly heat the surface of the glass until molten. Avoid allowing the inside to become molten or the glass will probably loose its shape during the following steps. Quickly change the flame to a strong reduction flame (excessive fuel gas, lacking in oxygen) and rotate the glass in it. The reduction frit should start changing within two seconds and continue to change for up to ten seconds. You must flame anneal the glass in this reduction flame. If you change the flame to a neutral or oxidation flame, the metallic raku effect will disappear and you will have to repeat the process. Powder covers the glass with a continuous luster. Large frit makes a broken, mottled pattern. Contains lead and therefore has a wider compatible range than other glasses. Reduction frit does not work with borosilicate (hard) glass, but does work with Effetre (Moretti) Vetrofond, Lauscha, Bullseye, Uroboros, Spectrum and Thompson Enamel. Note: When you change to a reduction flame, the flame will probably increase in length. Be sure nothing is in its way. Also, the flame will feel hotter to you, but it is actually a cooler flame to the glass. The cooler flame eventually stops the process because, the glass will cool and no longer be molten. The metallic oxides will not be able to get to the surface. This is why you must quickly change the flame to a reduction flame and immediately put the glass in it. Practice is required. Timing is very important. If you are not satisfied with the look, repeat the above procedure.
Q:: What Is Annealing? Why Is It Important?And How To Do It.? A:: Annealing is the process of making the entire glass item uniformly hot and holding that temperature steady long enough to remove all stress caused from the manufacturing process. The annealing cycle also includes cooling down slow enough so as to not allow too much stress to build back up.When glass is held at a steady temperature over a length of time, it is called soaking. Soaking the glass at a higher temperature has the advantage requiring a shorter soaking time for the stress to dissipate, but also runs the danger of being so hot that it may distort under its own weight or of sticking to something. The glass will also need to cool down a through a longer temperature range, and this will take longer than if it were annealed at a lower temperature. Soaking the glass at a lower temperature has the advantage of a shorter cooling time, but requires a longer soaking time to remove the stress, and, if soaked at too low a temperature, will not even remove the stress no matter how long soaked.After the glass has soaked for the proper length of time, all of the manufacturing stress will dissipate, but stress will reappear during cooling. What is important is that you keep the temperature steady for a period of time before slowly cooling the glass to room temperature. The annealing temperature we recommend for Effetre (Moretti), Bullseye and Lauscha glasses, is around 940º F. Use around 1050º F for borosilicate glass. Around 890º F for Satake. Using a temperature controller can maintain the temperature to within a couple of degrees. Manual control using an infinite control switch can not hold as tight a tolerance, but is adequate. This is one reason that we use annealing temperatures near the middle of the range. As the glass cools, the outside will always cool faster than the inside. As glass cools it contracts. If the outside of the glass cools much faster than the inside, the outside glass contracts faster than the inside glass. This variance in contraction causes stress in glass. Too much stress and the glass breaks. The slower the glass is cooled, the less the amount of temperature variance throughout the glass and less the amount of stress that will develop. The cooling of glass is most important between the annealing temperature and the strain point. As explained, glass will develop stress in itself through the cooling process. The strain point is a point in temperature at which any stress that develops below that temperature in the glass through the cooling process is only temporary. Stress that develops in the glass above the strain point is permanent. Once the glass has stabilized to room temperature, temporary stresses will disappear. The process to anneal glass once it is at the annealing temperature is as follows: First soak it for a period long enough to remove its stress. For a small bead, this can be as little as twenty minutes. For large beads, one hour. For a large paperweight, it can take half a day. Very large glass castings weighing hundreds of pounds can even take months. After soaking, cool the glass down past the strain point temperature slow enough so as not to allow too much damaging stress to develop. For a small bead, this can be as as fast as 600º F per hour (10º F per minute). For large beads, one half or one third that rate. A large paperweight, may require a rate as slow as 50º F per hour (less than 1º F per minute). Once the glass temperature has past below the strain point temperature, the cooling rate can be increased without causing permanent stress in the glass. However, cooling the glass too fast below the strain point temperature can still cause the glass to break during cooling due to thermal shock. You can anneal together borosilicate, Effetre (Moretti), Bullseye and Lauscha glasses. The temperature to use is 1000º F. It is a little high for all but the borosilicate, but at least 30º F below what any of those glasses will distort at. It is a little low for the borosilicate glass, but you can compensate for that by increasing the soaking time.
Q:: I am having problems with Mandrel Release. Am I doing it wrong? A:: To coat the mandrel evenly we recommend the following procedure: Hold the end of the mandrel loosely between your finger and thumb. Quickly dip the mandrel into the release and then quickly pull it out. Holding the mandrel this way insures that it will go straight in and straight out and make a round coating. If the mandrel is withdrawn at an angle, the coating may have a ridge down its length. The action of dipping the mandrel quickly causes the release to coat thicker. To coat the mandrel even thicker, quickly and continuously dip the mandrel in and out several times. The more you repeat, the thicker the coating. This is better than dipping, drying and then dipping again. Dipping the mandrel slowly applies a thinner coat. A mandrel with a very thin coating is harder to remove. Especially if the mandrel is bent. Turn the mandrel around and gently tap the end opposite the dipped end on the table surface. This gives the coating a very smooth surface. Turn the mandrel back around and vertically place it in a holder to dry. A container filled with sand works well. After coating the mandrel it is best to let it air dry. If your in a hurry, Mandrel release can be slowly dried in the very back part of the flame. Very important! Heat the mandrel until red hot for one full second in the area where the bead will be. This will happens best if the area of the mandrel release holding the bead has been heated until red hot before glass was applied to it. If a bead is ever difficult to remove form the mandrel, you most likely did not get the coating hot enough. When heated properly, the coating will lose its strength permanently after cooling. For this reason, apply glass to the mandrel while the coating is still very hot. It need not be red hot, but almost. If the bead ever spins off while you are making it, you probably did get the mandrel red hot but, then let it get too cool before applying glass to it. Once glass is on the mandrel, proper beadmaking techniques will assure that the glass will hold enough heat to keep the coating hot. If bubbles appear in the glass near the mandrel release, the mandrel release was probably not dried thoroughly.
Q:: Stringer Test for Glass Compatibility A:: Not everybody trusts this test but, if done accurately, can be a very reliable. Take two glasses that you want to test for compatibility. If they are not the same diameter, make them so. If you use unequal amounts of glass, you will get a distorted reading. The glasses need to be of contrasting colors in order to be able to work with them properly and to read the results of the test. Heat one end on both rods and then touch them together so that they align down their length. They should overlap about one inch. Now heat the joined area in the flame until they are completely fused together. Marver them round if necessary. It is very important that you do not twist. When the joined area of the glass is uniformly hot, pull it out into a stringer. Keep pulling the stringer, keeping it straight, until the glass hardens. Pull at least an 18" stringer. If you twist as you pull, you will cancel out any tell tale effects that would normally show up in non-compatible glasses. You can pull vertically to avoid the effects of gravity. When the glass cools, cut it to 12" long from the center of the pull. If the stringer bends by itself, the two glasses are of a different C.O.E and are not exactly compatible. When you heat glass, it expands. When it cools, it contracts. Glass with a high C.O.E. (coefficient of expansion) expands, and then contracts more than glass with a lower C.O.E. Since the two glasses were joined while molten, any differences in the amount of contraction as they cool and stiffen will reveal itself by bending the stringer. The glass that is on the concave side of the bend has the higher C.O.E. because it contracted more. If the curve falls away from a straight line too much, it may not be compatible for your application. Glasses used for beadmaking can have more curve in it than glasses used for fusing, especially large fused pieces. Opinions for the amount of acceptable curve range from about 1/4" to 3/4". To make this test more significant, you should also do a test to determine how close to the same temperature the two glasses soften, even when the stringer test shows that the glasses are compatible. The glasses are not annealed under ideal conditions and different glasses may cool and stiffen differently in the open. Make single color stringers from the colors to be tested. They must be identical in diameter and the same length. Place them next to each other but, not touching, in a kiln so hat they are held at one end. They should be parallel to the floor and elevated from it. This is easiest to do by pinching them between two kiln bricks. Heat them up slowly and observe the temperature at which each bends. If you heat them too quickly, the results may be distorted. For instance, black glass absorbs heat faster than white glass. If you heat up black and white quickly, the black glass will melt first, even if their melting temperatures are identical. For best compatibility, the bending temperatures should be within 50º F of each other. | GREAT IDEAS   |