Here is an article by Matt Maloney from Collector Glass News issue 114. (see article below)
there was also an article in issue 22 that had some descriptions of the process - I do not have a file for that issue but have the original, and can send a photocopy if needed.
Here is Matt's Article - thanks to Matt Maloney and Collector Glass News - PGCA newsletter
Characters on Glass by Matt Maloney Page 4
In the early 1900s, Decorated Glassware usually meant literally that. Decorations hand painted on glass articles intended for display, not everyday use. Utility glassware used for food packaging was typically plain except for its paper label. Most milk and soda bottles of the day couldn’t even have paper labels, as they were returned for sterilization and refilling.
A process for adding a durable color label to refillable bottles known as ACL (Applied Color Label) had been developed at the turn of the century that consisted of a paste-like compound of powdered colored glass, applied using a rubber squeegee through a screen of silk on which the desired design had been isolated. The decorated bottles were then re-heated to a specific temperature high enough to fuse the colored glass to the clear glass body, producing a permanently labeled bottle. But it was a slow and complex process and had seen very limited use until the mid 1930s. Then, thanks to simultaneous improvements in the process and Coke’s commitment to standardizing packaging among their bottlers nationwide, its use became widespread. Milk and soda bottles with increasingly complex and colorful ACL labels soon became the norm.
Other segments of the market began to recognize the advantages that variations on this process could provide for their products. Kraft Foods introduced Swanky Swigs; decorated, “free” drinking glasses used as the containers for some of its dairy products. Other food packagers followed with their own designs or “novelty” themes. But all of these were new designs of the packager’s creation, not reproductions of an image already recognizable and appealing to customers.
That changed in 1936, with the seminal licensing deal between Owens-Illinois Glass and Walt Disney. Suddenly, even small, local food processors, using packaging supplied to them by O-I, could associate their goods with the popular Disney characters. They were a hit with the public, and the category of Character Glassware was off to a strong start.
Other animation studios soon created sets of glasses featuring their own characters. Porky, Daffy, and Elmer from Leon Schlesinger Productions (soon to be purchased by W.B.), Popeye and Betty Boop from Fleischer Studios; Mighty Mouse from Terrytoons; and other early charcters exist on glasses. But apparently without similar use as packaging, as they are far less frequently encountered today.
Countless other small volume Character Glass promotions have existed since then, but in 1953 Welchs provided widespread distribution of characters on glass once again when they licensed the Howdy Doody Show’s cast for use on their product packaging. Over the next 50 or so years they would go on to license numerous other characters to feature on their glasses.
In the mid-70s, Pepsi distributed a massive volume of Character Glasses in record short time with their Fast Food tie-ins. Glasses that a few years later would become so common and so ubiquitous at flea markets everywhere that one dealer I knew referred to them as “cockroaches”. He’s gone now, and so are the 50 cent glasses.
That was the peak of the Character Glass Era, and we know it. But it was great to have experienced it, to continue collecting the glasses that were produced in the earlier days, and the ones that will continue to be produced - if in somewhat more “restrained” quantities - in the future.
The more glasses I collected and the more familiar I became with their details, the more curious I became about the methods and materials used in their manufacture. Interestingly, it was the defects and the errors among those Pepsi-sponsored glasses that gave me my first insights.
The occasional glass with one color far distant from its correct location, or missing completely, meant that the image had been printed one color at a time. That explained the existence of imperfect registration – but not the method by which registration was accomplished. I had noticed that on some commercial packaging with painted-on labels, there was a square indent molded into the heavy glass bottom that I assumed was a positioning key; but glasses had no such device. Then I saw an error glass with what looked like a herd of Road Runners, four in total, with some of them partially obscuring the others. That glass had obviously gone down the line twice and proven that the starting position for the image was random. Also, looking at the image from inside the glass, it was possible to determine the order in which the colors had been applied. With the Pepsi glasses, it was almost always white first and black last to provide the outlines that tied the other colors on the character together (hopefully). It also revealed the neat trick used on the Tweety glass. To make 3 colors look like 4, they applied the yellow over white in some areas and not in others where it looked darker. I always liked that, and disliked the “half-tone” method they used more frequently; dots of black applied over a solid color to make it look darker. That only worked well at five feet away without your glasses on.
I have always liked the look of 70s Pepsi glasses with their heavily applied glossy colors and thick black outlines that display so strongly and look so “cartoony”. Clearly, other glasses that followed them from other sources were produced on more sophisticated machinery using different printing compounds, though. The Star Wars glasses of 1977-1983 took the overlaid color trick to new heights, applying colors obviously designed to allow the one underneath to show through, creating a new color. Five or six colors applied in a complex pattern of overlays looked like twice as many (try looking at THOSE glasses from the inside). The McDonalds/Topps baseball card series took it to the level of photorealism. I recently read a manufacturer’s ad touting their ability to screen print any shape bottle or glass in four colors with a registration of +/- .015mm using optical registration. There are even specialty systems that use a printhead for printing directly to an object. But for the majority of volume production, even on today’s highly automated and sophisticated machines, the use of screens to apply the image remains one element that hasn’t changed that much..
I saw a film of a four screen machine in use that looked much like what Dave Leonard, the man who put together the Pepsi promotions, described in an interview back in CGN#22. It was a semi-automated four screen system that probably would have produced glasses with the traits we have come to recognize in those 70s glasses.
Glasses fed in horizontally were grasped firmly by the machine one at a time, and moved into position on rollers below the first of four screen trays. The trays were four sided and several inches deep with a screen as their bottoms, and contained just a half inch or so of a colored paste – each one different. Each screen had been prepared with a wax or resin applied to its surface everywhere except where elements of the design were to be printed in one color. Operating automatically within each tray was both a paddle that spread a thin coat of color evenly over the screen’s entire surface in one direction, and a squeegee operating alternately in the opposite direction. The glass was brought into contact with the screen from below and rotated in sync with the squeegee moving across the screen from above, forcing the colored paste through the finely woven fabric and onto the glass in the desired pattern for that color.
Still held by the machine, the glass moved into position below the next screen tray, and the process was repeated until all the colors in use for that design had been applied.
While in operation, an attendant would add colored paste to the trays as needed throughout the run, which was a minimum of 21,600 glasses (600 cases) for the 70s Pepsi promos. Understandable, as shorter runs would not have been cost effective at the 10 to 18 cents these glasses were reportedly wholesaled for. Setting up a different run required significant down time on the machine before production could begin again. There was squareness of each screen within its frame, alignment of each screen’s position with each other, color application and glass handling that all had to be just right to meet a quality control standard of “as good as possible”.
Aha! Perhaps that explains another observation. If you’ve ever hunted for a better copy of a character glass to replace the off-register one in your collection, you have probably discovered that many other copies “out there” share the same problem. Shades of difference between them perhaps; a fraction more or less off, but the same color out of line in the same direction over and over again. If the mis-registrations were the result of sloppy handling of the glasses by the machine, wouldn’t the errors be more random?
I’m inclined to suspect that the pressure to fill massive orders rapidly or lose them to a competitor, for a customer whose main concern was reliable supply of an adequate product at an incredibly low price, was the culprit behind what appears to have been some less than ideal initial setups.
And I find that my attitude toward those registration-challenged 70s Pepsi Character Glasses has softened somewhat. I’m not perfect either. If that’s what it took to make it all happen, I can live with it. At least until I come across one from a better batch, LOL.
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