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Cone 6 Silky Matte

Code: G1214Z
Modification Date: 2019-05-08 15:33:01

This glaze was born as a demonstration of how to use chemistry to convert a glossy cone 6 glaze into a matte.

MaterialAmountUnits
Wollastonite27.0g
Ferro Frit 312436.0g
EPK20.0g
Calcined Kaolin14.0kg
Silica5.0g

Alert: This recipe contains units of measure, it cannot be imported into Desktop Insight as is.
You must recalcuate it to percentages and then to the total you need (if it has not be done here).

Firing Schedule

Rate (F)Temp (F)Hold (Min)Step
100220601
300173302
1082195153
1502095304

Notes

This is a calcium matte. As such, it develops its visual effect by the crystallization of calcium silicates (which depends on the melt being quite fluid, or runny). A fortunate side effect of the calcium matte mechanism is that additions of colorants and opacifiers can produce very interesting visuals that vary with thickness and firing cooling rate (which gets potters excited but which industry avoids because of the difficulty in maintaining consistency). However cutlery marking can be an issue with this type of glaze, especially for slower cooling kilns (where more crystallization occurs).

The spirit of this recipe originally was to demonstrate the main difference in the chemistry between a matte and glossy glaze, the SiO2:Al2O3 ratio (and how it can be changed to adjust the degree of matteness of a glaze). We documented this as a 'textbook approach' to understanding the chemistry of a matte glaze (it was done by adjusting the chemistry of a glossy as a use-case for early versions of Digitalfire Insight chemistry software during the early 1980s). That recipe jumped from computer screens to actual use and has been employed around the world since by artist potters and even industry (especially tile).

Higher levels of MgO (as opposed to the CaO in this one) produce the other main type of true matte glaze (also well melted yet matte), the surface of these is "wavy" and has a silky feel (as opposed to this calcium matte which has a smooth micro-crystalline surface). Like calcium mattes, MgO mattes produce more matteness with slow cooling in the kiln. Consider testing the G2934 MgO-matte recipe beside this one to determine which is best in your application. This one, G1214Z, can work well on certain clay bodies and it can give a smoother surface. As with all mattes, be sure to control the rate-of-cooling in production firings (and match it to that done during testing) to get the intended degree of matteness. Remember that you can adjust the chemistry to produce more or less mattness (by lowering and raising the SiO2:Al2O3 ratio).

This recipe was changed in Mar 2019 from 37 EPK to 20 EPK and 14 Calcined Kaolin (you can make your own calcined kaolin by roasting EPK powder in a bisque container at 1000F). The previous recipe was shrinking too much on drying (causing cracking).

Out Bound Links

In Bound Links

XML to Paste Into Insight

<?xml version="1.0"?>
<recipes version="1.0" encoding="UTF-8">
<recipe name="Cone 6 Silky Matte" keywords="This glaze was born as a demonstration of how to use chemistry to convert a glossy cone 6 glaze into a matte." id="3" date="2019-05-08" codenum="G1214Z">
<recipelines>
<recipeline material="Wollastonite" amount="27.000" unitabbr="g" conversion="0.0010" added="0"/>
<recipeline material="Ferro Frit 3124" amount="36.000" unitabbr="g" conversion="0.0010" added="0"/>
<recipeline material="EPK" amount="20.000" unitabbr="g" conversion="0.0010" added="0"/>
<recipeline material="Calcined Kaolin" amount="14.000" unitabbr="kg" conversion="1.0000" added="0"/>
<recipeline material="Silica" amount="5.000" unitabbr="g" conversion="0.0010" added="0"/>
<url url="https://digitalfire.com/4sight/recipes/cone_6_silky_matte_3.html" descrip="Recipe page at digitalfire.com"/>
</recipelines>
<urls/>
</recipe>
</recipes>


By Tony Hansen




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