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low fire mason stains / slips

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Im working with terra-cotta (cone 04) for hand built plant pots. I'm interested in a creating a wide range of colors to add to their surfaces before firing. I have been firing once (no bisque firing) and using a white slip i created through help from this site (although the original post i've lost) and am very happy with the results. The mixture i've used is 25% Kaolin/EPK, 25% Ball/OM4, 25% Custer Feldspar and 25% Flint. So that's good, i have terra-cotta pots with white decorations that after firing remain matt, and porous, exactly as i'd imagined. Now i'm interested in expanding my surface treatments from just white, to include a wide variety of colors. I previously experimented with a black slip, (terra cotta body, water, iron oxide) but found it wasn't stead fast after the firing. I know there are mason stains on the market and engobes neither of which i'm formiliar with. My thoughts were, If i could understand what the four agents in the white slip where and how they functioned, i could set up my own mixing lab and understanding the characteristics of each element, create the slips i'm looking for. That means from my understanding, i will need a low firing (cone 04) white bodied clay to form the base for my colored slips. Then i will need the coloring agent, (this part i need help on) and then whatever else it takes to make the slip stable and suitable for my purposes. After researching the four ingredients of the first white slip this is what i've found:

Kaolin/EPK= mined in florida, a white bodied clay, good for casting not for throwing.

Ball/OM4= (Old Mine #4, Mayfield, KY) A fine-grained ball clay* with excellent plasticity and strength.

*a clay noted for its plasticity. used for the manufacture of clay pipes allowing for thinner ceramic walls.

Custer Feldspar= Im unclear on what this stuff is or does. it seems to be a type of potash. It seems to come from the mountains of north dakota.

Flint= It looks like flint when ground to a fine powder is used as a filler.

I'm comfortable with my understanding of colors having studied painting and color theory while in school. If i could establish a few variants (for mixing purposes) of the primary colors (red, yellow, blue) then i could probably figure the rest out (saturation, hue, tint etc) on my own.

In a nut shell, i'm looking for the basic principles of colored slip making from which i can begin my experiment, which i will be happy to photograph and share with anyone interested.

thank you,



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I use a Val Cushing low fire stain formula of 1/3, 1/3, 1/3 epk, 3110 and stain.

Your formula may be a more versatile slip. If it works for you, that is what counts.


The stain formula is for wiping on and accenting texture.

The Custer Potash feldspar is a flux with naturally occurring sources of silica and alumina. That is what Feldspars are...in the case of Custer Feldspar the flux part is potash.

Go google a reference chart for Mason stains. They are made of complex formulas. The reference chart advises what will work with particular stains, what their limits are for temperature, and whether they can be used for engobes or slip or as glaze colorants. They also recommend what types of chemicals should be avoided with certain colors. Some like zinc. Some don't. Others may look great with calcium carb/whiting.

So read these, know what fluxes are in your glazes and coordinate.



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One issue you might have with using Mason Stains is that they are not rich and dark at Cone 04. Color brightens and darkens the higher they are fired.

Higher concentrations will not help much ... I use upwards of 25% stain in some cases and the colors don't pop at low temp.


One idea that might or might not be worth trying is Amaco Velvet underglazes ... I know, the name is misleading since they can be used perfectly well over stuff too.

I leave my jars of underglaze open until they get thick as yogurt then use them as slip.

The colors are great at 04 ... http://www.amaco.com/shop/category-49-low-fire-cone-05-glazes.html

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