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Cold Mold Ripple in Glass Bottles

Cold Mold Ripple Sample [1]

Cold Mold Ripple Sample

It has always seemed strange to me that people started calling a *Cold Mold Ripple* something different than what it really is. Bottle collectors and sellers use the terms *Whittled *and *Hammered* to define what they see in the glass bottle. I haven’t found it referred to as this in the older books, but maybe they didn’t pay that much attention to it earlier. It seemed to come up in the newer books written after about 1927. I think the condition started when they changed from wood and brass to using cast iron for the bottle molds. This appearance is really the difference in the glass wall thickness. One also might explain it as an attempt to make people think the bottle they were selling came from a wooden mold. Thinking that the mold had been whittled with a sharp knife. I think it is time to start rethinking these terms.

Earlier American Historical Flasks didn’t have Cold Mold Ripple, until they departed from the cast brass shell molds that were used to make them in. When they started making them in cast iron molds, they started having the variable thickness in the glass.

These early molds were made in regular cast iron. These molds were also made with greater wall thickness than the early brass shell type molds. The characteristic of forming a bottle by blowing it in the mold; requires that the bottle maker has to create a required shape and size of the first stage of the bottle (the parison shape). This form was critical to having the bottle being blown, to produce a proper distribution of glass wall thickness in the walls of the blown bottle.

This savvy of parison design, size and shape was a bottle maker’s secret knowledge. When I went into the glass industry in the 1950s, this savvy could help a mold engineer direct changes needed to correct the distribution of glass in the bottle being made. If he had that knowledge he could almost select the numbers in his paycheck. Today the whole concept of this problem has been taken over by computerized parison shape design.

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Now then back to the condition of *Cold Mold Ripple.* The early cast iron molds were cast against the sand in a casting flask box. There was a wooden pattern used to create the cavity part of the mold and a wooden pattern to create the outside form of the mold casting. These molds were basically had Grade “A” type of graphite in the iron. I touched on this in my blog, regarding Chilled Cast Iron Mold Cavities. The difference here is that the earlier cast iron molds were not used repeatedly in a fast enough cycle to build up enough operating heat in the molds. A higher temperature was needed to help the glass blow tight and evenly in thickness in the mold cavity. When the parison glass was blown against iron that was too cold, it didn’t let the glass flatten against the mold face, thus the bottle wall had a variation in thickness. This is what makes the glass have a difference in light translucence and what makes it look wavey or rippled like the surface of water when a pebble is thrown into it. If one measured the thickness variations in a broken shard of glass wall material, you would find this difference in thickness.

The whole process of making a bottle free-formed (F-F) by hand, or blown-in-a-mold (BIM), or made on an automatic bottle machine (ABM); each method has a major reliance on controlled heat loss in each phase of the glass forming. The starting temperature of the molten metal (glass) and the temperature needed for each effort to do anything with the forming of the glass, is temperature sensitive. The magic touch of the earlier bottle-maker’s work, thrills me when I get to study an old bottle and marvel at the products they made. Bottle designs were always changed as they had problems where their ingenuity could not correct the condition they were fighting when the bottle was blown. Venting, straps on flasks, champhered corners, scalloped corners and many other concepts were used to solve these problems. Heal tap in the bases of early square medicine bottles was one problem they had a hard time to overcome. Sometimes the shoulder blow-up in the mold was a big problem. Almost every hand made bottle fascinates me.

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Now back to the term *Whittled,* I have tried to point out that this wasn’t even done in the wooden mold. It didn’t even exist in the early brass shell molds – so why do we use it?

First of all, I happen to have three bottles that I am confident were made in wooden molds. One is a demijohn made in a two-part mold that came about half way up the shoulder. At the start of the shoulder curve there were three large vent holes in each half of the mold. One of the holes must have become plugged when this bottle was blown, so there is dimple in the glass almost three inches in diameter and three eighths of an inch in depth, where the glass didn’t blow up against the mold surface. I am confident that this wooden mold was machined to its original shape, but the mold seams only come up about three inches on the shoulder and the rest of the shoulder is free formed with the neck. The cavity walls have areas where loosened carbon fines were cleaned off , that give the body neat characteristic patches of diameter change. It should also be noted that the two main mold seams are raised more than they would be in an iron mold – again suggesting wooden mold burn-off.

This bottle has a nice large blowpipe tubular pontil on it with one side about a half inch long. There was a wooden bottom plate that the mold halves closed around. The bottom seam is set in about an eighth of an inch from the mold diameter at the base and it provided the basic push-up with a contact radius ring around the bottle base where it rests on a surface.

The entire bottle has a mottled surface that makes me think they used a coating on the charred wood surface to protect the wood. It could have been any number of materials, but it was no doubt bee’s wax with sulfur powder in it. What ever caused the mottle, it is not Cold Mold Ripple.

My other two wooden mold bottles were early medicines and the differences in the shoulder height of the upper corners from burn-out is obvious when you compare them. Their surfaces hinted of a coating and there was no Cold Mold Ripple condition, but actually the bottles are probably too small to have it.

In the 3-part molds the dip cast iron part of the mold often had a base ring on the base of the casting and boss iron protrusions on it to hold the vertical hinge pin for side swinging shoulder sections. The base of section of these bottles is usually full of cold mold ripple in the glass while the shoulder-molded section of the bottle is often free of the ripple effect. The shoulder sections had less iron mass and therefore ran hotter than the dip mold base,

Since retirement I have spent a lot of time studying SARATOGA Mineral Water Bottles and I knew that they had changed to chilled cast iron in the time zone of 1862 to 1864, because the bottles stopped having as much Cold Mold Ripple in them.

Another interesting thing is that the Cold Mold Ripple is normally horizontal in the glass. On three occasions I have found it to be vertical and one of those was only vertical on two vertical panels that were on each side of a flask type bottle.

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Now to get back to the *Hammered *description; it just isn’t done in a mold unless it is required to crate a rough cavity or a stippled cavity for the glass to look frosted or have a special surface. Therefore I can’t see how it applies.

Then to be equally ridiculous, no one hammers in a bottle mold unless your want to obliterate an area of lettering that is no longer wanted. Even then it is best done with a riffle file or a round steel cutter burr. Any thing you do in the cavity of the mold will make a mark on the glass. I have some examples of early mold repair done in the 1850 to 1900s where they milled out a section of iron and filled it in with weld. That is a subject that I will be covering in a blog, on the repair of bottle molds. My problem is that there wasn’t much written on this subject either.

When I came into the industry to work, I had to question the: who, why and when; they started chilling the cavities of cast iron bottle molds. I was also at a time, when they put the mold equipment on flame tables to pre-heat it before it went on the glass machine. If the equipment lay on that table of flame too long, they cooked the hell out-of-it and caused a lot of fire cracking in the cavity iron. These marks can be found on early ABM bottles, but I have never found them on hand blown bottles. The machine production speed and the table preheats was just too much for the iron. We made molds out of many different metals to study the effects of different alloyed metals for their resistance to this damage and to evaluate the glass surface qualities produced when it was blown against the different metals. That too is a different subject to cover.

Red Matthews [2]

[3]PATENT: Improvement In Glass Molds [4]

Click here for the Patent PDF

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