Striking Northstar Borosilicate

NorthstarŽ BorocolourŽ is currently available in 54 colors in rod, 24 colors in frit and 22 colors in powder form. Some of these colors are affected by heat. We call these "striking" or "re-heat" colors for they change color when reheated (i.e. Yellow is in clear glass rods when you receive them from the factory. But when heated to the annealing temperature [about 1050°F or 560°C], they change or "strike" to their new color). Other colors may appear pink, blue, green or amber before striking. (All RUBIES are shipped pre-struck to ensure color uniformity.) The longer you strike a color, the darker the color becomes until the saturation point is reached. If, after striking, the glass artist heats the glass to the working temperature again, NorthstarŽ BorocolourŽ returns to its original un-struck condition. This process of striking and reworking may be repeated many times. The transparent colors are obtained more easily if struck in an electric kiln. Work your piece as hot as possible (but do not boil) and place it in your annealing oven while it is in the un-struck condition. Striking may be performed in your torch flame as well, preferably in a neutral to slightly oxidizing atmosphere. Avoid striking the glass at too high of a temperature. Using either method observe the glass while it is being struck. It is possible to control how dark your pieces become by carefully controlling the striking time. The striking process may be performed simultaneously with the annealing process.

Please note that some colors will strike at slightly different rates. For example, NS-05 Orange will take longer to strike than NS-07 Ruby. If you have many different colors in the same kiln this could cause Ruby to become darker than you want while you are waiting for the Orange to strike. If this is a problem, you can strike differently colored pieces in separate firings of the kiln or, if you are using many different colors on a single piece, keep watching during the striking process and begin to cool the piece when you are satisfied with the effect.

The darker, more intense, striking colors begin to strike more quickly and will be darker when saturated. The darker colors are easier to strike in the torch flame, but on the other hand may become very dark if struck for a long period in the annealing oven. Some of the lightest color variations may take longer to strike in the flame yet can be held at striking temperature for long periods without becoming too dark. A higher annealing temperature will strike NorthstarŽ glass more quickly. A slightly lower annealing temperature will strike the color more slowly. In general, a lower annealing temperature used over a longer duration is better for striking. Please avoid accidental slumping of your pieces!