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Reduction Glass

Reduction glass reacts to a reduction flame setting producing a raku like effect, often with metallic overtones. Reduction glass is usually in the form of rod, frit (granulated) or powder. Glasses that are formulated and sold as a reducing glass will have a different and desirable look after they have been reduced. Their look before being reduced may still be desirable. Some glasses not sold as a reducing glass may also reduce, but usually with undesirable results. Reducing is achieved in the flame and is accomplished by subjecting the glass, while molten, to a reduction flame atmosphere.

To use, make the entire glass item in a neutral flame from the reduction glass, or, as is more common, apply the reduction glass to the surface of a compatible glass base. When using frit or powder, the use of a marvering pad, frit tray or frit trough is very helpful. Completely melt the glass and bring it to its final shape.

One method of reducing the glass is to to simply cut back on the amount oxygen or increase the amount of the fuel gas while working the glass in the flame. Experiment with different ratios to find the best flame setting for you and your burner. This first method is less intimating and tends to yield a darker and less metallic look then the second method.

The second method is done by completely turning off the oxygen flow and increasing the fuel gas until it actually pushes off the face of the burner by as much as several inches. This makes a clean flame and will prevent soot from accumulating on the glass. Place the molten glass fully within the base of the flame. This large flame setting may seem hot to you, but in fact is not hot enough to keep the glass molten. The reduction process begins within a couple of seconds and is finished when the glass is no longer molten, usually ten seconds or less, dependent upon how hot the glass started out. Because this flame setting is so cool, it can also take care of the flame annealing.

Practice this kind of flame setting before using it on your glass. Adjust the burner to this kind of flame setting with the glass not in the flame to prevent the glass from becoming dark as it tends to in the first method described above. If the fuel gas is increased too much the flame will blow out. Turn off the gas before relighting. Also, reduce the flame until it comes back in contact with the face of the burner before turning on the oxygen or it too will blow out the flame.

Any reduced glass put back into a neutral or oxidation flame will become unreduced and the process will need to be repeated to get it back. Darkness produced from the first method described is usually permanent.

What is a Neutral, Oxidation and Reduction flame?
A neutral flame has a perfect balance of fuel gas and oxygen as supplied through the burner. An oxidation flame has more oxygen supplied to it than the fuel can consume. A reduction flame does not have enough oxygen supplied to it through the burner and must get the balance from the atmosphere. The chemistry of a reduction flame can have dramatic effects on molten glass.

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