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  1. Crystalline Glaze Chemistry Several have inquired about this specialty glaze in recent months, so I thought I would post an introduction into crystalline chemistry. The very first thing to do with this glaze is: throw out your glaze calculator and UMF spreadsheet: they do not apply to this glaze nor can you bring it into unity. Basic cone 6 through 10 crystalline recipe is: 50% ferro frit 3110, 25% zinc oxide, 25% silica 325m, and a seeding agent (see later). ^ Lithium carbonate flux additions discussed later. This is the basic crystalline glaze recipe, regardless of what cone you are firing to. However, crystalline glaze requires high fluidity of the glaze, so a high cone five is the minimum temperature level. It can be fired under five, but it takes a fair deal of chemistry to achieve it; so perhaps later it will be discussed. The reason you see so much variation in this basic recipe is because so many variables effect its outcome. Most of the variations are artistic preferences being inserted to control crystal size, population, and growth patterns. Likewise, the wide variance in firing ramp holds are due to kiln size, crystal development, peak cone temperature, and in many cases because the kilns were never calibrated by using cone packs or pyrometers to adjust thermocouple readings. An example: a ramp hold is stated as 2002F, but that same temperature could be 1992 or 2018F in your kiln. Frit 3110 is the standard and most reliable frit used in the crystalline recipe. There are frits used such as Fusion Frit 644, and others. If Ferro Frit 3110 is not available in your region, then use the chemical analysis of 3110 as a guide to compare available frits. Match the chemistry of your available frit as closely as possible to the chemistry of frit 3110. 50% of the basic recipe is frit, it alone makes up the glassy matrix of the glaze. Although silica is being added to this recipe, that silica addition serves a specific function other than being a glass former. Yes, the silica will add to the glass content, yet it is being added for feedstock for crystals to form. Frit is ground up glass that has already been melted at high temperatures; so the chemistry required to form glass in a glaze is not a consideration. Crystalline glaze requires a thick application of glaze, and crystals require a thick layer of molten glass to grow in. So lowering the frit level in this basic recipe also means you are restricting the glass level in which they grow. You rarely see the level of frit deviate from this basic recipe, and when it is adjusted: those adjustments are minimal. Crystalline glaze or crystals are chemically known as zinc-silicate crystals. Crystals form an ionic bond between zinc and silica: which is why equal parts of each comprise the basic recipe. Yes zinc adds opacity to the glaze and silica is a glass former: but neither addition is present in the recipe for those reasons. Zinc and silica are added and adjusted to form crystals, the additional glass formed or opacity added are secondary reactions. So the adjustments you see in various recipes are to manipulate crystal growth and population, and secondary “glaze chemistry†is not a consideration. Nerd (TJA 2017) Edit 8-12-2017 for spacing and grammar. Edit 8-13-2017 Explanation of temperature in first paragraph amended.
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