Cutting strengthened glass

A method of cutting a sheet of heat strengthened glass having its major surfaces in compression and its interior in tension, by means of an abrasive fluid jet, comprising supporting the sheet upon one of its major surfaces, directing a highly concentrated fluid jet into which abrasive particles have been introduced against the other major surface of said sheet at a first, lower cutting pressure on the order of 10,000 psi to initially penetrate the sheet without causing venting and chipping of the heat strengthened glass along the initial cut, substantially increasing the pressure of the fluid to a second, higher cutting level on the order of 30,000 psi after the initial penetration, moving the abrasive fluid jet relative to the sheet of glass along the desired line of cut with the cutting pressure at the higher level, and establishing the line speed of the fluid jet relative to the glass at the second cutting pressure so as to produce a smooth cut wherein the adjacent heat strengthened glass is free from vents and chips.