In addidition to the seasonal frenzy, this week saw me in the depths of Lewisham doing a 3 day course on glaze technology.

I have been mixing glazes from recipes for ages, but never really understood what all those mysterious sounding materials were, what they did or how they interacted. One of hte simple – but surprisingly effective things we did was to fire a whole range of materials on their own.  materials slab This slab contains:


  • Nepheline syenite
  • Calcium borate frit
  • Bone ash
  • Borax frit
  • Alkaline leadless frit
  • Lead sesquisilicate frit
  • Lead bisilicate
  • Cornish stone
  • Potash feldspar
  • Soda feldspar
  • Flint + talc
  • Flint + dolomite
  • Flint + whiting
  • Flint + colemanite
  • Flint + zinc oxide
  • flint + potash feldspar
  • Flint + soda feldspar
  • Flint + cornish stone

Of the first 10 only the Bone ash didnt really work at all, some were underfired, and some like hte lead boiled over – demonstrating the need for mixing of silica + flux + alumina. For most of 11-20 I tested flint (silica) plus various fluxes. The other attendee tested quartz as the other available silica (and had a lot less successs…).

We tried varying degrees of zirconium in a basic transparent gloss glazeher mixes (below, top row: clear transparent, transp + 5% zirconium, Transp + 10% zirconium (to test its opacifying qualities – pretty subtle in the pic and in real life). The second row is the same transparent with (L) 5% chromium oxide and (R) 5% chromium oxide + 5% rutile – which has gone bubbly and changed colour slightly.

Next we chose printed recipes to make up and test, both worknig from the Potters palette book as it had colour pictures. This book offers a small number of basic glaze bodies to which various oxides are added for colour.  “1 below is the plain body. 22 and 23 are two variants the other attendee made with  varying proportions of copper oxide and rutile (3% + 3% and 1.5% + 5% respectively.) I rather like number 23 and it behaves interestingly around the contours of the test piece.

flicks glazes


I made up a blue/grey glaze that used 0.25% cobalt oxide and 0.5% nickel oxide. That was fun with the scales trying to measure such tiny amounts! Here’s the results on the left below. I then tested it with lots of different oxides either below (L) and above (R)  the glaze to see how they behaved:

  • cobalt oxide
  • black iron oxide
  • chrome oxide
  • iron oxide spangles
  • turquoise oxide
  • coral red stain on white and buff clays
  • rust oxide
  • copper carbonate
  • manganese dioxide again with white and buff bodies

more oxides




oxides 2

And finally, I had been reading about volcanic glazes and asked about them so she got out some silicon carbide (mixed 1:10 with china clay) that was painted un under the glaze, and some ilmenite (also mixed 3:1 with china clay). Here’s those results. They dont photograph very well but give some interesting textures and cause some interesting reactions in the glaze. The text I was reading suggested mixing various weights of silicon carbide into the glaze which gave a more or less intense result.

volcanics etc 2


I came away feeling inspired by the colours and textures that can be acheived – and feel a lot more tests coming on in the new year!

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