How Glass Blocks Were Made
To avoid collecting duplicates, I created a Catalog of my glass flower frog collection. Annotations note dimensions and other characteristics of identification. Photos from multiple angles present the shape.
Over my first year of collecting I purchased a few near-duplicates that only varied a little in size or shape, yet I assumed they came from different moulds. It was only after I learned how glass flower frogs were made that I understood that such variations are possible from the same mould.
Also, I was curious about the broken glass found around the holes on the bottom of most glass flower frogs. eBay sellers occasionally point this out as a defect, but it's almost always present so I knew that couldn't be the case.
This is the manufacturing process based on the Cambridge Patent:
You will more fully understand the process as you review the illustrations, photos, and text, below.
The patent, copied from the United States Patent and Trademark Office database, provides a detailed explanation of the manufacturing process: Cambridge Patent PDF
The upper illustration shows the complete mould with the plunger inserted; the bottom illustration shows the inverted block without the mould.
This illustration shows three different mechanisms for holding the inverted block. Note that the glass has fallen, creating a peak on the top of the block.
Read the text: Cambridge Patent PDF
This Westmoreland Glass Company mould belongs to Greg A. Jennings, who acquired it from Charles West Wilson, grandson of one of the co-founders of Westmoreland.
The wood handles were added for ease in demonstrating how the mould works, and are not original.
The plunger is inserted through the molten glass to form the holes.
The open mould
The familiar shape of a Westmoreland block bottom with rectangular feet
This Westmoreland flower frog is a perfect match to the mould shown above. You can clearly see that the bottoms of the conical shafts of the plunger were smaller than the holes in the mould. This explains the seepage of the glass around the conical shafts, which is broken off after the block has cooled.