Originally Posted by LBJ
>>Is the colors obtained strictly by the amount of precious metal being fumed and applied? Or is it a combination of the amount of fuming being applied AND flame applications?<<
The color obtained is widely variable, and can be influenced by any combination of the following factors:
Temperature and color of the underlying glass
Flame chemistry
Distance of the glass from the originating "flume" of metal
Temperature of the fuming rod itself
Humidity and studio temperature
Other factors that you will discover as you go
Think of the torch flame as an inverted funnel, with the torch head being the small base end of the funnel. If you imagine the flame being forced up through that funnel, it's easy to see that the flame and heat is going to be most focused at the center, and most diffuse and turbulent around the perimeter of the funnel. The focused part is a given, but considering the complex and turbulent behavior of the heat around the edge of the funnel is harder to understand. Because the vaporized metal is being carried swiftly upward by the movement of the hot air (but at the same time is constricted and spinning against the outer layer of cold air), the further out of the center the piece to be fumed is, the more scattered the deposition of the metal. This has an effect on the optical quality of the micro-thin deposition of metal will be. Personally, I like the diffuse appearance. A sharper, harder deposit can be achieved near the center of the heat cone, but it's also more challenging to maintain, because that same heat wants to either burn off the metal (gold) or basically tarnish the metal (silver). I'm sure you've already discovered it is possible to put on gold and then burn it back off again almost completely. The silver doesn't burn back off as easily, but it does change and take on more of a cloudy, silvery appearance.
>>>Silver likes reducing flames and Gold likes oxidizing flames.
With that stated, would a neutral flame be used for Rake-n-Comb or clear encasement to minimize the loss of either fumed metals?<<<
The reducing/oxidizing is a bit of an over simplification in my experience, although that's essentially correct. I have not had good luck trying to deposit fume in a truly neutral flame and I don't really know why. If you get that figured out, please let me know how you did it!
But if I understand you correctly, you are wanting to develop a bimetal fuming? If that's the case, you can either encase over the subsequent layers, or you can very carefully develop the color outside the central cone of heat. I have had good luck putting on a thin layer of gold, followed by a heavier deposit of silver, and then another layer of gold to get to the desired color. The base fuming of gold seems to help light come through the silver and the second layer of gold sort of sinks into the silver to make a warm, soft peach color. I didn't care for the look of encasing between fuming, it looked clumsy to me and didn't allow the two colors to mingle.
>> Is the metal used for fuming to be placed right at or near the flames candles?
yes ~ at the tips of the candles, far enough up that it doesn't stifle the flame or rob it of oxygen. If your fuming looks dirty, you were too far into the candles.
>>Lastly, could have sworn I read somewhere that the target material (tubing) needs to be approximately 6" away from the metal which is being fumed?
That has not been my experience. There is a sweet spot where the flume of metal vapor is strong and the glass is hot enough to grab the metal vapor but safely outside the zone of the vapor being blown off again by the flame. I'm sure it would be very different depending on what torch you are using. Using both a Minor and later a Lynx, I normally found that sweet spot to be 3" to 4" inches above the fuming rod and about 1" to the outside edge of the flame from the rod, so kinda diagonally away from the flame but still well within the hot zone. If the glass is too cold, it won't grab the metal vapor (looks good but rubs off after the piece comes out of the kiln) if the glass is too hot, it seems like the vapor just slides past the glass and is wasted. Strangely, fuming was significantly easier on the Minor, so I think the sharpness of the Lynx flame was most likely the problem. I learned to adjust the flame chemistry and my fuming position to compensate, but it is harder to do.
I hope that helps!
p.s. If there is an authoritative reference on fuming, I've never seen it. I'd love to read a more scientific explanation of the process.
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