Once you are comfortable with the flame settings it is important to know what colors should be worked in what flames. Refer to the provided guide for specific flame settings for a particular color.
In general, most borosilicate colors should be worked in oxidizing flames. The Cobalt colors, the Rubies, and all other striking colors are susceptible to reduction. If worked in a reducing flame for any great duration these glasses will discolor and lose their appealing hue.
With the Cobalt colors, they streak gray, with the copper Rubies they turn a milky red, and with the silver base colors they turn a foggy cream color. This discoloration is due to a chemical reaction that is caused by un-burnt gas in the flame.
What happens is the gas particles search for oxygen in order for combustion to take place. In doing so, it robs the surface of the glass of oxygen. This causes the metal oxides that are bonded to these oxygen molecules to change valence state and deposit on the surface in the elemental form of the metal. This deposit causes the discoloration to occur. By increasing the oxygen content in the flame these problems can be eradicated. This is the key in keeping the colors brilliant and true.