Glass Break Tool
Medieval Glass Break
My friend Conor O Ceallaigh came to me at the Cloisters rem faire demo and asked me if I could make him a medieval glass break tool. He had been researching it, and had a vague description of what it should look like based on it's usage. I had planned on making a lot of hooks for the demo , but this seemed like a lot more fun. So I took the information that was in Conor's head and put that to work.
I started with a railroad spike, which I just happened to have brought with me. I started by forming the tip. After narrowing it out to the size and shape Conor described I worked the metal down to about a 3/8’ round for about 4”. Then a forge the center down to about a 3” rectangle, which was supposed to act as a heat sink, (more on that later). I then forged the top down to round taper for handle.
The process took about two hours of forging time. I took the tool home and cleaned it up in the shop.
I was quite excited to see how it would work. Making a tool based on description.
When Conor tried to use it, the design proved a failure. He heated up the tip, but by the time he brought it to the glass it was already cold.
We decided the heat sink must be closer to the tip. So I went back to the drawing board with more information from Conor and made version 2.
Again made from a railroad spike, this time I created a slightly narrower point and started the heat sink right above it.
In the 12thcentury, they ground chalk in a lead pot and added water to it. Then, using brushes made from from theail of a marten, badger, squirrel or cat or the mane of a donkey, traced the outline of the pattern onto the glass. A piece of glass, slightly larger than the finished size was placed on top of the pattern board and the outline of the piece was traced onto the glass using the chalk and water mixture with one of the brushes that were made. If the glass was too opaque and the pattern couldn't be seen through it, the outline of the piece was traced onto a piece of clear glass. When the chalk was dry on the piece of clear glass, the piece of opaque glass was placed on top of it and both pieces were held up to the light and the pattern lines transferred to the opaque glass with the chalk and water mixture.[1]
After this, take a lead pot and in it put chalk ground with water. Make yourself two or three brushes out of hair from the tail of a marten, badger, squirrel or a cat or from the mane of a donkey. Now take a piece of glass of whatever kind you have chosen, but larger on all sides than the place in which it is to be set, and lay it on the ground for that place. Then you will see the drawing on the board through the intervening glass, and, following it draw the outlines only on the glass with chalk. If the glass is so opaque that you cannot see the drawing on the board through it, take a piece of [clear] white glass and draw on that. As soon as the chalk is dry, lay the opaque glass over the white glass and hold them up to the light; then draw [on the opaque glass] in accordance with the lines that you see through it. Delineate all kinds of glass in the same way, whether for the face, the robes, the hands, the feet, the border, or any other place where you want to put colors.
The process of cutting glass was, to say the least, very adventuresome in the 12thcentury and the glass craftsman had to be very experienced. The glass craftsman used a tool made out of iron with a wooden handle fitted over the tang of the tool. The "business" end of the tool was tapered on two opposite sides and came to a chisel point. Theophilus provides these intriguing instructions for cutting glass.[2]
Next heat on the fireplace an iron cutting tool, which should be thin everywhere except at the end, where it should be thicker. When the thicker part is red-hot, apply it to the glass that you want to cut, and soon there will appear the beginning of a crack. If the glass is hard [and does not crack at once], wet it with
[1]De Diversis Artibus. Book II, chapter 17, second paragraph.
[2]De Diversis Artibus, Book II, chapter 18, first paragraph.
saliva on your finger in the place where you had applied the tool. It will immediately split and, as soon as it has, draw the tool along the line you want to cut and the split will follow.
Let me just say that you can crack a piece of glass with heat. I’ve done it plenty of times by accident with my soldering iron.
Figure 6- 12th Century Glass Cutting Tool
It’s not clear when the diamond was first used as a tool for cutting glass. However, it was in use by the 14thcentury in Italy and is mentioned with other hard stones in Antonio da Pisa’s treatise, Il Trattato di Antonio da Pisa Sulla Fabrricazione delle Vetrate Artistiche.[1]
Diamond-cutting is a more convenient method, which leaves a straighter edge, and seems to have spread gradually during the course of the 16thcentury, and must have been especially useful for cutting plain quarry glazing.[2]
Glass Cutting Techniques in the 20thCentury
There are several different ways to transfer the pattern to a piece of glass in the 20thcentury. These include:
1. Gluing the piece of the pattern to the glass with rubber cement.
2. Tracing the outline of the pattern piece onto the glass with a marker.
3. Holding the pattern piece on the glass while you score the glass.
4. Placing the pattern on a light table, the glass over the pattern and scoring.
Which technique the artist uses depends on the artist's level of expertise and confidence in their glass cutting ability.
We, in the 20thcentury, have a much easier means of cutting glass. It's called a glasscutter. Actually it should really be called a glass scorer since it really doesn't cut the glass it just scores it. In its simplest form, a glasscutter is held in the hand. A tiny wheel made of carbide steel is run along the pattern line and it scores the glass. The glass is then "broken" along the score line either with another tool or with the hands. This is known as running the score, and the tool that might be used (instead of the hands) is called running pliers.
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