Q - Can you tell me the annealing schedule for your glass?
A - For a complete review please look at Bandhu’s book Contemporary Lampworking, chapters 8 (Vol 1) and Tables 1 and 3. In general a small piece, (less than 1/4 inch at the thickest point) you should soak for 15 minutes at 1070°F and come down no faster that 1.95 degree per minute until you reach 910. After that you can increase the ramp down to 7.5 degrees F until you reach 400°F. In practice it is a good idea to follow the first ramp rate until you hit 850°F then speed up to 7.5. After you hit 700°F you can double the down rate and in most cases that would allow shutting the kiln of. Remember not to open the kiln until 400°F or lower.
Q - I am currently a Masters student in the Center for Imaging Science - Color Science. I was wondering how you deal with color and QC. Do you make spectral measurements of the glass? Do you keep databases of spectral data to watch for trends? Is it possible to characterize (spectrally measure) the "pigments" in order to predict color mixtures? Really, I am just curious about how Glass Alchemy scientifically deals with color.
A - There are instruments that can make these measurements but the industry is to small to justify the expense. We have considered building our own but haven't found the time. For now the standard in the industry is to have several target rods. If the color falls in between the target colors, accept it; if it does not, reject it. We loosely track trends in color shift along with some weather data. We save pieces of rod for future measurement. Weather seems to be more important than the source or purity of the pigment. For example, with the Crayon colors, the color can shift from yellow to orange or red from one day to the next.
Q - I just started playing with my GA boro sample set today. I am using the lynx center fire of a GTT Delta Elite with propane and tanked oxygen. I followed the instruction in the "Setting a Neutral Flame Card" that was included with the set. I then tested it with the sample of 987 Amazon Night. As you can see from the attached pictures the Amazon Night rod (rod on the far left) remained unchanged which means that I have a neutral flame. I then put the sample of 786 Triple Passion in the same spot in the flame where I tested the Amazon night. As you can see from the attached pictures, the Triple Passion (rod in the middle) has a shiny metallic surface, but is purple inside which is the color it is supposed to be. Where did the shiny metallic surface come from? The same thing is happening with 383 Silver Strike 3, which is the rod on the far right in the attached pictures. It was supposed to turn a brownish color and it did, but there is a shiny metallic surface on the top as well.
A - The metals come to the surface at about 1200 - 1300°F. In a reducing flame you get an oil slick effect. In an oxidizing flame you get a clean, pure metallic effect. From your photo it appears that your flame may be slightly oxidizing, not reducing. I have only seen this in the studio one other time. My guess is you held the last two pieces about a 1/2 to 1 inch further out from the torch head than the 987. Your “neutral zone” may be very narrow, especially on a GTT which tends to burn the propane very well and generally doesn’t have a problem of over reduction like some other torch designs. If your O2 regulator is in the 35 - 45 psi range I would close down the center knobs about 1/16 to 1/8 turn to increase the working zone. I think this should keep the glass from going metallic on you.
Q - I am in the process of moving my studio.I will be having to reset up everything. Do you have any advice on the ventilation? Is there a type of fan or specific piece of equipment I should use? Any other advice or thoughts you may have that you think would be helpful would be much appreciated.
A - There is some great info in this manual. It is overkill but will be valuable info in making your decisions. Basically you don’t want to try and vent the room. Rather you want some general ventilation for the room to keep the air fresh and exhaust any fumes not captured by the main system. The main system you want to create a cubical that your torch is in and vent that area. This is cheaper and requires a smaller quieter exhaust fan. Set it up so that you can easily replace a burned up fan. You should be pulling about 150' per minute by your face. To measure this without a very expensive device use a piece of tissue about 1/2 inch wide and 6" long and hold it by the tip of the torch and determine if it deflects about 45 degrees. That said if you spend many hours on the torch every month this is important. If you spend 2 hours on the torch 15 degrees many be enough.
