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Blowing - Technical Notes for G109 & G1095

G109 – Chalcedony

Characteristics: This is a highly reactive color that can produce a variety of effects and colors, when exposed to the right conditions. The color, upon purchase, usually looks brown, tan, or grey, with maybe a hint of green or purple. It is not until this color is reintroduced to heat that the gaffer will begin to be able to determine the result of effects that this very versatile color will deliver.

How to work: The objective is to achieve the vibrant variations that occur when the silver is burned off the surface, revealing the other, more appealing characteristics of this color: purple, blue, green, red, orange, and yellow. So, how do we do that? We have to get the G-109 hot enough that the silver that has deposited itself onto the surface of the glass burns off.

I have obtained the best results by applying one to three layers of the G-109 frit (depending on desired opacity,) to the last gather of glass. I then apply heat to the glass using an oxygen/propane torch because the temperatures that this torch reaches exceed those produced in the glory hole, and thus help facilitate an easy burn-off of the silver haze deposit that we view as the brown, tan, and grey. If you are unfamiliar with using oxygen fed torch,

there are three types of flames settings:

Reducing: When there is more propane than oxygen.
Neutral: When there are equal parts oxygen to propane.
Oxidizing: When there is more oxygen than propane.

The flame setting that we are interested in is the last one - the oxidizing flame. This is the hottest flame setting, and the one that will heat the Chalcedony up enough that the color will “reset” itself to a new color setting (i.e., it will have burned off the silver deposits on the surface.)

So, what we do is set the torch to a “raging-hot” flame and heat up the color till it looks clear. Once it has gotten this hot you want to quickly cool it on the marver, or spot-tool it with the tag, or tweezers, or what ever you prefer using. The tooling will tell the color to cool down quickly which will keep the silver from coming to the surface and stop it from producing the brown/tan effect. If you partially tool the glass, this will create a differentiation of temperatures between the areas cooled and not cooled, and these differences in temperatures will create variations in color.

This is how to begin the color process, but because this color has such a wide range of effects and colors, you can continue to develop different results with the use of the oxidizing flame setting on the torch. When you re-expose the color to the flame setting you can, essentially, begin to “paint” the color by using the flame heat as your “brush.”

Variables effecting resulting colors:

The distance between the torch head and the glass. You are trying to create a temperature range in which the Chalcedony will be able to grow the specific crystals that produce the visible color. If you hold the torch very close to the glass you will see the heat turn the color back to clear. As that area begins to cool it will “reset” that place in the glass back to its starting point – purple. If you hold the torch further away it will get it hot, but not as hot, and not as quickly, and will result in a different crystal formation represented by a different visible color.

The duration of time that you expose the glass to the heat is an important determinant in which colors will be produced by that given heat exposure.

How quickly the glass is cooled after being heated is also a huge contributing factor in color variations.

Run your glory hole at a neutral flame setting. It is important that you are keeping your glory hole from running rich (i.e., turn the gas down to the point that there are no flames escaping the door of the hole. This will keep the silver from coming to the surface and depositing itself there.

Hopefully this information will give you a basic understanding of how this color works, and a place of origin to go about learning the many beautiful variations that this color can produce.

To begin: Start your exploration of this color with a small one gather bit, and follow the aforementioned process and techniques. Take notes at the beginning of your exploration and anneal each of the color samples so you can have a record of how you achieved your results and if you want to repeat them. The more you work with these concepts, the easier it will be for you to achieve the results you desire.

Please share your results and feel free to ask any questions I may not have covered.

Good luck and good work!
Mike Hengler

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