How to Make Homemade Underglazes

how-to-make-homemade-underglazes-new
The truth is, I was a nerdy ceramics undergraduate student. I wanted to learn everything, right away -— and I loved my glaze calc class. No, really, I did. I took a ridiculous amount of notes and then put them all in plastic sleeves in a binder. I’m sure I tested every recipe I could find or invent. After discovering commercial underglaze, I was sure I could make that too.

In today’s post, an excerpt from our latest freebie the Underglaze Users Guide: How to Use Underglazes to Add Color and Graphic Interest to Your Pottery Projects. I am sharing my adventures in homemade underglazes, and my underglaze recipe too! – Holly Goring, Associate Editor, Pottery Making Illustrated and Ceramics Monthly. This item originally appeared in the January/February 2012 issue of PMI.


Smooth, silky, perfectly opaque, commercial underglaze is that wonderful substance that coats and colors both greenware and bisque ware with ease (I’ve even seen it work on mature cone 04 earthenware), and without flaws. And, in terms of color, what you see is what comes out of the kiln, no guessing, no hoping. They are dependable as well; covering large areas quickly with smooth and consistent brush painting. They take light-colored, transparent or clear glaze very well without dissolving into the glaze during the firing. Finally, commercial underglaze fires into a hard, unscratchable surface without pinholing or flaking from cone 04 all the way to cone 10.

Commercial Underglazes

Today, most commercial underglazes are formulated using frits, which reduce shrinkage, allowing them to be applied to both greenware and bisqueware. They are produced using a colloidal process. A colloid is a substance microscopically dispersed evenly throughout another substance (think mayonnaise or hand cream). Underglaze manufacturers use a chemical process that employs a high-shear mixing technology to create colloids. The substance created does not settle and cannot be separated out by ordinary filtering or centrifuging like those in a typical suspension. This allows for complete integration of all raw materials, including the colorant, during the base mixing stage.

Developing the Recipe

Variations of underglaze recipes were available on the Internet but not much could be found in textbooks, beyond iterations of slips (clay suspended in water, formulated to fit either to wet or dry greenware) and engobes (generally a lower clay content, most often fits greenware and bisque ware ). Few of these recipes encompassed all the characteristics I was looking for—something similar to commercial underglaze. Not too much to ask, right?

I started by choosing a clay and a flux. I needed a fairly heavy clay content for adhesion to the clay body, and an equal amount of flux to lower the melting point of the silica, and to create a hard surface. My clay choices included: EPK kaolin, calcined kaolin, OM-4 ball clay, and talc, all fairly white firing as to not add to the color, and each contributing something different to the adhesion needed. My fluxes consisted of: Ferro frits 3124, 3134, and 3195, a good place to start in terms of readily available frits. Then in a radical move, I ignored all previous instruction and treated the colorant as one of the base ingredients. This allowed for full incorporation of the color with the other two ingredients during the mixing of the base recipe. I used commercial stains in order to get an opaque quality (I later tested variations with oxides that resulted in a somewhat transparent underglaze.)

I mixed 1000 gram batches in a thousand variations (or something close to that). I actually mixed three batches of each recipe to testing gums and suspenders, without which, any substance mixed from the above ingredients would settle to a rock-hard mess and be nearly impossible to brush onto any clay surface. I tested CMC gum (powder, premixed into a liquid), premixed bentonite, and Sta Flo laundry starch (a tip from one of the internet recipes).

Not having the ability to replicate the colloidal process, I sieved and ball milled each recipe in order to fully integrate the raw materials into each other and to reduce the particle sizes as much as possible. (Note: Do not ball mill recipes with zirconium-silicate inclusion stains, as ball milling will destroy the inclusion that renders these stains non-toxic.)

I tested each glaze on leather-hard, bone-dry, and bisqued earthenware and stoneware test tiles. I fired the earthenware tests to cone 04 and the stoneware tests to cone 6 and cone 10, all in an electric kiln.

After many firings and many eliminations, this recipe came very close to replicating commercial underglaze:

Sieve all materials with an 80 mesh sieve and then ball mill for at least 12 hours . Incorporate Sta Flo Laundry Starch until the mixture reaches a thin yogurt consistency and sieve the entire mixture again .

Pros and Cons

The results were good, very good—smooth, creamy, good adherence, versatile at all temperatures, a hard surface, and an intense color. The substance worked well on both clay bodies and in all stages, but was best on bisque ware. Brushability was best with the Sta Flo. I found that too thick of an application caused flaking and pinholing. The lack of sieving and ball milling did the same. If mixed to the correct consistency, one coat was sufficient while two coats often was too much. The colors became muted when fired to cone 10 but still held up in hardness and adhesion. Only small batches could be mixed at a time due to the inclusion of the Sta Flo, which is organic and caused mold to grow in the bucket within a few days. The mold could be skimmed off but added unwanted lumps if it wasn’t all removed. And of course the amount of commercial stain to produce the rich colors similar to commercial underglazes was ultimately very expensive. In the end, mixing this homemade underglaze was a lot of work for a product the manufacturers do just a bit better, faster, and cheaper. However, if I want colors that aren’t available commercially, now I know how to make them.

You can receive great technical information like this along with intermediate to advanced techniques in every issue of Pottery Making Illustrated.

Comments
  • Enormously impressive, Holly. All ceramicists understand patience, but you take that to another level. And exactitude and focus. Even though I’m unlikely to try to emulate you, you teach us a lot about ingredients and their implications. I use underglaze only, for my large ceramic garden sculptures (on white or buff stoneware, applied at greenware stage – I fire direct through to 1200 without bisquing). You take this to the level of a high art.

  • I have made my own underglazes, slips, and glazes.
    I used a Warning 2 speed blender to do fairly small batches..up to 200 grams.
    I’ve gone through 3 of these blenders up to date.
    Very rarely have I had to sieve.
    Although they are for food they work really well and cut down your mixing time.
    I’ll look forward to using some of these underglazes!
    JMR

  • Great post, my kinda girl! Thank you because a post like this takes away the scary stuff and empowers those of us who are open to a bit of extra trial and error to develop our own unique finishes. THIS is why I read CAD emails ski avidly. Thank you.

  • I am wondering if you could share the results of your experiments with suspension agents other than Sta Flo… I like the availability of the starch but want a better shelf life… What did you learn and what did you use?

  • I am so impressed, Holly! I have printed out recipe and instructions, and I do intend to try this myself!

  • Try adding some vinegar to the Sta Flo Laundry Starch.
    Raz

  • nice work!.

    I live on a small island in the Caribbean, and it s nearly impossible to got the things Holly Goring used to make under glazes.
    So I invented the next very simple solution.
    for translucent under glaze mix mason stains, with hot water stir or sieve the batch ,and some drops of slip dope stir or sieve after cooling ! works great.
    If you prefer a covercoat, add a little clay slip to it.

  • Ball mill did you just have one laying around???

Enter Your Log In Credentials

Send this to a friend