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.
|Ferro Frit 3124||36.0||g|
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).
|Rate (F)||Temp (F)||Hold (Min)||Step|
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).
G1214Z blue glaze from Lilly Ann Hume
G1214Z golden glaze sample from Lilly Ann Hume
1214Z over Ravenscrag slip at cone 6 gives mottled surface
These are two cone 6 matte glazes (shown side by side in an account at Insight-live). G1214Z is high calcium and a high silica:alumina ratio (you can find more about it by googling 1214Z). It crystallizes during cooling to make the matte effect and the degree of matteness is adjustable by trimming the silica content (but notice how much it runs). The G2928C has high MgO and it produces the classic silky matte by micro-wrinkling the surface, its matteness is adjustable by trimming the calcined kaolin. CaO is a standard oxide that is in almost all glazes, 0.4 is not high for it. But you would never normally see more than 0.3 of MgO in a cone 6 glaze (if you do it will likely be unstable). The G2928C also has 5% tin, if that was not there it would be darker than the other one because Ravenscrag Slip has a little iron. This was made by recalculating the Moore's Matte recipe to use as much Ravenscrag Slip as possible yet keep the overall chemistry the same. This glaze actually has texture like a dolomite matte at cone 10R, it is great. And it has wonderful application properties. And it does not craze, on Plainsman M370 (it even survived a 300F-to-ice water IWCT test). This looks like it could be a great liner glaze.
True functional mattes have fluid melts, like glossy glazes. They need this in order to develop a hard, non-scratching durable glass. The mechanism of the matte on the right is high Al2O3 (G1214Z), it is actually melting more than the glossy glaze on the left (G1214W).
Double-layered on top half. Fired with the PLC6DS schedule.
The glaze is G1214Z matte base and the clay is M390. 5% zircopax was added to the glaze on the left (normally 10% or more is needed to get full opacity, the partially opaque effect highlight contours well). 5% tin oxide was add to the one on the right (tin is a more effective, albeit expensive opacifier in oxidation, often only 4% is needed). The PLC6DS firing schedule was used.
The glaze is G1214Z cone 6 base calcium matte. 5% titanium dioxide has been added. This Plainsman M390 tile was fired at cone 6 using the PLC6DS firing schedule. Titanium can create reactive glazes, like rutile, even with matte surfaces (provided the glaze has good melt fluidity). Calcium mattes host crystallization and work particularly well. Because titanium dioxide does not contain iron oxide lighter colors and better blues are possible than with rutile. Like rutile, the effects are dependent on the cooling rate of the firing, faster cools produce less reactivity.
Out Bound Links
This glaze was developed using the 1214W glossy as a starting point. This article overviews the types of matte glazes and rationalizes the method used to make this one.
Takes you on a detailed tour of how to start with a glossy glaze, compare its chemistry with a target formula in the light of what kind of chemistry matte glazes have, then alter the chemistry while a...
A glaze that is not glossy. Of course, unmelted glazes will not be glossy, but to be a true matte a glaze must be melted and still not glossy. To be a functional matte it must also resist cultery marking, clean well and not leach into food and drink. Thus it is not easy to make a good matte glaze. I...
A base MgO matte glaze recipe fires to a hard utilitarian surface and has very good working properties. Blend in the glossy if it is too matte.
2014-03-26 - A cone 6 boron-fluxed MgO matte developed at Plainsman Clays by Tony Hansen (a link below will take you to its page there). This page contains technic...
In Bound Links
This is a base transparent glaze recipe developed for cone 6. It is known as the 20x5 or 20 by 5 recipe. It is a simple 5 material at 20% each mix and it makes a good home base from which to rationalize adjustments.
The process we used to improve the 20x5 base cone 6 glaze recipe
A recipe developed by Tony Hansen in the 1980s. Its was popular because of the simplicity of the recipe and how well it worked with chrome-tin stains.
2003-12-17 - This is also known as the 20x5 recipe. It was developed during the early 1980s to demonstrate principles of glaze chemistry in creating a glaze base s...
Substitute for low expansion cone 6 G1215U, this sources MgO from talc instead of a frit
2013-05-29 - During 2013 we saw problems with the G1215U low expansion glossy that we had been recommending from some years. It was not melting to a completely ult...
Plainsman Cone 6 Ravenscrag Slip based glaze. It can be found among others at http://ravenscrag.com.
2014-02-20 - This works well on Plainsman M340, but especially on a whiteware like M370. Produces an ivory white with some fleck. The surface is very silky, remini...
<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">
<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"/>
By Tony Hansen