Developing glazes

After our glaze tutorial with Dave I was itching to get on and start to mix up my own glaze recipe.  I did my first set of tests at home mixing up a glaze to the following recipe:

Talc                           37
Potash Feldspar     18
Wollastonite             4
Quartz                     14
China Clay              27

This was a recipe for a celadon glaze taken from the book Colour in Glazes by Linda Bloomfield.  Although this would need a reduction firing to produce the classic blue/green colour I happened to have the red iron oxide at home and thought it would be interesting to see what kind of results an oxidation firing would give.  To keep things simple I decided I’d start off with 1kg of the dry materials and carry out a line blend test, commencing with the equivalent of 0.4% of the red iron oxide.  Instead of measuring out the base glaze into separate pots, I used one large pot of the base glaze and then increased the oxide amount after each test pot was glazed.  The red iron oxide was added in the following proportions: 0.4% (+4g), 0.7% (+3g), 1% (+3g), 1.4% (+4g), 1.8% (+4g).

The results looked like this:

WhatsApp Image 2018-05-22 at 15.11.28 (1)WhatsApp Image 2018-05-22 at 15.11.27

Overall the glaze worked quite nicely.  It didn’t run or crawl, had a nice sheen to it and gave good coverage.  It produced an oatmeal to pale brown colour as the amount of oxide increased.  I’m not sure that these colours will be particularly useful for my project but it was great to practice mixing up the base glaze and interesting seeing the results and gradation of colour produced.

A little while after this I began mixing up some more glazes at uni.  This time I wanted to produce a matt/satin glaze as opposed to gloss and look at one with a colour that I felt might be more useful for my project.  I chose the following recipe from Stephen Murfitt’s, The Glaze Book:

Potash Feldspar           45
Dolomite                        22
Quartz                            16
Zirconium Silicate       11
China Clay                       6
+ Copper Carbonate     2

I mixed up 2kg of dry ingredients (minus the oxide), added water to make a single cream consistency and then sieved it through an 80 mesh sieve.  The whole amount was then weighed out and split between 10 small pots, giving 276g of glaze per pot (slop weight).  I decided to try three different oxide percentages out here just to see what difference it would make, testing with 1%, 2% and 4%.  In this instance that meant adding 2g, 4g and 8g respectively, into three pots.

WhatsApp Image 2018-05-22 at 16.11.15WhatsApp Image 2018-05-22 at 16.12.02 (1)WhatsApp Image 2018-05-22 at 16.12.02 (2)WhatsApp Image 2018-05-22 at 16.12.02 (3)

Using three more test pots of  the same base glaze I decided to add a mixture of two different oxides – manganese dioxide and cobalt oxide, again in different strengths.  These are all mixed up and ready to go but unfortunately my test tiles hadn’t been bisque fired, as there’d been a problem with one of the kilns at uni, so I’ll have to wait it bit longer before I get to see the results of these concoctions! Overall I’m really enjoying the alchemy of glazing.  It’s very exciting waiting for the kiln to open to see how successful the tests have been.  At the moment I’m favouring the use of coloured slips for the effects I intend to produce on my plates and bowls, but I’m sure there’ll also be a place for the right glaze too, for some things, and it would be good to have them on hand when the time comes!


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