Vintage Carnation cream top milk bottle with label. The label is of the sort refered to by collectors as red pyroglazed.
The red part of this is fairly self explanatory but pyroglazing is an interesting process. Obviously there is an intuitive part of this in that heat was used in the process. But what process? Basically pyroglazing is a type of stenciling where lead, silica and borax were fused to the glass at a temperature of 1200 degrees Fahrenheit, over the course of four hours. This process was introduced in the middle 1930′s and helped enhance brand recognition and deter theft by other dairies.
The bottle stands 9 3/4 inches tall, held one quart and bears an intriguing little embossed mark near the base. The mark is a triangle and within that triangle is a 7 and the letters MINN.
Some resources indicate that this is a symbol used by the Liberty Glass Company, which was founded from the remains of an earlier company in 1918. In addition to the triangle mark they also typically marked the bottom of their bottles with an embossed LG and a year mark. Ours does not have the LG mark but bears a 12 inside a circle and the number 46. Presumably then this bottle was made in 1946.
As an interesting aside, Liberty glass used Lustro-Color as the trade term for their colored label process.