Funstuff: Proving the Myth of Cuban Glass

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This is an experience that I made during New Year festivities in at home in Germany. My cousin is a big fan of a particular Cuban Rum brand and got some “Cuban Glasses” as gift from someone else. The story behind Cuban glass is curious. Under Castro and his current replacement the average population in Cuba chronically appears to lack of something, in this case it was cocktail drinking glasses. The myth is that using a piece of heating fan wire and an old motorcycle piston ring and empty rum bottles, creative Cubans were able to cut their own glasses from empty rum bottles. This heroic procedure actually made it into the Havanna Club advertisements, as shown below.

After a long new year’s dinner and being reinforced with an industrial strength drink, my uncle, a retired physics and biology teacher, and I decided to actually bust or prove this myth with the bottle that was emptied earlier. Unfortunately, we did not have a fancy rum bottle ready, just an empty advocaat bottle to prove the concept. Trying to get as close as possible to the myth, we got a piece of heating fan wire from a broken fan, a couple nails and a piece of wood and model-train transformer and later on grandpas old radio transformer.

The nails and the piece of wood were used to build a support stand for the bottle, because we did not have the piston ring to align the heating wire. The idea is to wrap the heating wire around the bottle to enforce a clean crack in the Glass from the tension caused by the temperature gap where the heating wire sits. Note that using a regular wire is not going to work because the resistance is too low to convert current into heat.

The first attempt shown in the above picture with a model transformer resulted in nothing but a slightly charred label. The voltage delivered by the model train transformer (approx. 20V) was not enough to provide enough power to actually crack the class. Fortunately, we still had grandpas’ old radio transformer that he used to build and test his home radio equipment several decades ago. Most of the components he used in that transformer predate WWII.

The voltage on that transformer is freely adjustable between 0 to 250V and we made the glass crack at around 50V, incidentally setting the wooden support-stand on fire (a piston ring would have been more appropriate).

The edge on the glass followed exactly the line of the heating wire. Because it was not smoothly aligned you also see this misalignment in the crack.

Alternate Approach
The success got me curious and I started digging through some old books for other examples of the act. There is actually another workable procedure for making these classes, documented in an old WWII book (see references). According to the notes, you could actually “repair” broken bottle necks by filling the empty bottle with oil (e.g., engine oil or vegetable oil whatever was available during the war) take a glowing piece of hot iron (i.e., a rabble that was heated in the fire) and stick it into the oil. That would ignite the oils surface at an instant and the glass would crack exactly at the fill line of the oil. Then you could blow out the flame and try it over at another broken bottle.

Conclusion
Overall we considered the Cuban glass myth to be true. The next step to create a professional grade glass would involve sanding the edges of the crack to create a smooth surface (this is also shown in the Havanna club ad). The act provides a dangerous but workable framework to create any kind of glass that you would want in the household. Some people use alike techniques to create feeding bowls for their pets or artistic creations. This act involves significant risk, be sure to be safe or not perform this act at all.

References:

• Havanna Club Advertisement
• Bönicke, Gerhard: „Tornister-Lexikon für Frontsoldaten“, Tornisterschrift des Oberkommandos der Wehrmacht, Abt. Inland : nur für den Gebrauch innerhalb der Wehrmacht, 1943 (In English: Bönicke: „Tornister Encyclopedia for Front-Line Soliders“, Memo of the Wehrmacht supreme command for domestic affairs: only for Wehrmacht use, 1943)