Sandra Ratch, M.A. April, 2022
I do not want anyone to think I am criticizing Bill Lockhart or suggesting that he has not contributed greatly to the knowledge of bottle making in the 20th century. On the contrary, without his work, we would have little information to go on. Here, I just think I found a better theory to explain this strange mark on the bottom of this bottle. (Bill Lockhart has read this post and agrees with what I've found).
In 2010, Bill Lockhart described a bottle found in El Paso that had an odd mark on the base (https://sha.org/bottle/pdffiles/EPChap7b.pdf, p. 252, Figure 7-23). You can see that the mark is two concentric circles, offset from the bottle and at 1+ cm apart from each other. At the time he could not attribute a machine to the making of this bottle.
Lockhart 2010 (2000):252
This same bottle was again discussed in another Lockhart (N/D:7) publication and the O'Neill 1911 patent was ascribed to the bottle. The image below shows a valve on the base of the final blow mould - this valve would draw the glass down to the bottom of the mould. Lockhart suggests that where the two arrows are seen (below) is where the two mould seams come from. He also suggests that the offsetting occurred with the blowing of the bottle. However, this should make a mark where the two concentric rings are closer together, or the outer one is not visible at all (because the valve is the moving part and the outer portion fits very tightly into the base plate). It should also not be so offset if it is created in the final mould.
Lockhart N/D:9
The composition above could, I suspect, cause concentric mould seams that are closer together, but the amount of asymmetry of the marks in comparison to the bottle would be less as this is occurring in the final mould, not the blank mould. I suggest instead that the outer part of the valve was tight-fitting and did not cause a seam, creating a valve mark with no concentric ring around it (or a less obvious one), and more centred.
Having read Lockhart's article (N/D) recently and having it in the back of my mind, I came across
O'Neill patent US1217102 from 1917.
1917 O'Neill Patent 1217102 Figures 4 and 5
Within this patent, You can see the blank or parison mould (9) and above it a valve (108) and a mould closure (15) that houses the valve. From this drawing, you can see that the interior circle would come from valve 108, and the exterior circle from where the mould closure (15) comes in contact with the glass. It would then be transferred to the final mould where the blowing would be completed. This would create two symmetrical seams (valve and mould) reasonably distant from each other and together off-centre to the same degree (as in the top photo). Valve 108 allows air into the blank mould to force the glass into the finish mould (14), and is then left open to allow air to escape which the parison is blown from below to fill the entire blank mould before being transferred to the final mould.
I do believe this 1917 patent explain's Lockhart's soda bottle better than the 1911 patent.
Please contact me if you think I am incorrect on any of this.
Sources:
Lockhart, Bill
2010
Bottles on the Border: The History and Bottles of the Soft Drink Industry in El Paso, Texas, 1881-2000. Originally published online in 2000. Can be found here:
https://sha.org/bottle/References.htm
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