A Hemingray made glass block will always have a "Plant 86" code on it. Plant 86 is what number Owens-Illinois gave to the Muncie factory after they bought it, (86 was on the blocks and 26 on bottles). These are the only glass blocks that are made by Hemingray. There is one exception to this that we will get to further down the page. Here is one example of what the embossing will look like.
Plant 86 Embossing example
The exception to this is the plant code 86 is on the blocks that were used in the Hemingray factory buildings. They didn't have a plant number on them. There are two possible explainations for this 1. these blocks were experimental and were being tested in the buildings on the Hemingray property 2. These blocks were only meant to be used at the factory.
Example of a block with no plant code used at the Muncie plant
Hemingray Blocks for the most part have only 2 different sides. The "welded" block I believe is a prototype (found in the Hemingray dump and don't have a plant code).
These blocks were both dug up at the Hemingray dump and were used on some of the buildings on the grounds. The one on the left shows what the "weld" looks like the one on the center shows what it looks like after the cement covering was put on. The one on the right is what the standard production block looks like.