A basic recipe for crown glass from an 1881 book, "The Household Cyclopedia of General Information," lists ingredients for crown glass as follows: 60 lbs. of white sand, 15 lbs. of nitre, 1 lb. borax, 1/2 lb. of arsenic, 30 lbs. of pearlash (potassium carbonate).
Today, boric oxide is added to crown glass to make borosilicate glass, which gets rid of chromatic aberration. Barium oxide replaced iron oxide in optical crown glass as it does not alter the dispersive power in lenses as iron oxide does. Fluorite, zinc oxide and phosphorus pentoxide are common additives as well.
All the ingredients for the crown glass are placed in a furnace and heated to a temperature between 2600 and 2900 F.
After the sand and other ingredients melt into molten glass, the glass craftsman affixes a mass of hot glass onto the end of the hollow tube called a blowpipe and blows a small puff of air into the pipe to start the glass bubble. The hot mass of glass is put back into the furnace and as the blower continues blowing, he creates a balloon of glass. He removes the glass from the oven and shapes a flat bottom on the balloon.
The hot glass balloon is transferred to a solid rod called the punty (sometimes called a pontil) rod. The punty has a glob of hot glass on its tip that attaches to the flattened end of the glass at the opposite end from the blowpipe. The blowpipe is broken from the glass, forming an opening which, when the punty worker puts the glass back in the 2400 degree furnace to heat up again, will begin to expand outward. As the glass bubble is heating up in the furnace, the punty rod is turned, starting slowly and gradually turned faster to create a larger bubble. The glass artisan then spins the punty and glass steadily around in the air or rolls the punty along a bar. The centrifugal force pushes the glass bubble out into a flat plate usually around 3 feet in diameter.
After the glass plate or disc is formed, it is allowed to cool slightly, and the punty is broken away. Then the disc is taken to a 1000-degree kiln to continue cooling slowly and to strengthen and harden the glass.