Posted in Experiments, Sculpture

Ceramic Tests

Another side-track for the course, but before I can finish the Annie Peaker, or other ceramic, work I need to do a set of glaze tests so as to know how to approach colouring and Glazing them. This needs to be completed carefully and rigorously if the results aren’t going to be disappointing.

The following notes illustrate the process.

Prep

Tile conceptMade 24 test tiles with ES40 hand build clay. Numbered 1 – 24 on back. Slab roller 3+1. Texture on front and curved.

Slip

700g ES40 clay, soaked into water to make a slip. Added 1L water. Went through soak-stir etc until I had a decent slip. When ready poured into a bottle to be used later.

Stability

Some tiles quite unstable. Used the Surform to take the bottom to level. Seems to have solved it, but needs consideration in future. (Small lug on back?)

Available colourants

Slips from Bath Potters Supplies: Autumn Brown. Black. Azure Blue. Lime Green. Crimson. Sun Yellow.

Oxides:

  • Cobalt Carbonate/Oxide (1-5%) Blue
  • Black, Red, Yellow Iron Oxide. (2-12%) Straw, Honey, Greens, Black, Brown, Red
  • Copper Oxide/Carbonate. Nickel Oxide. (2-6%} Brown, Green, Pink, Yellow
  • Titanium Dioxide. (3-12%} White
  • Manganese Carbonate/Oxide. (4-12%} Mauve Brown
  • Tin Oxide.(6-10%} White

Percentages are dry weight additions. I.e. 1% is 10g dry oxide added to 1kg dry base.

Also: White Decorating slip.

Oxides to colours and percentages, Michael Bailey, Glazes Cone 6. p22.

Possible Tests

  • Slip only, single and double dipped.
  • Watered down slip. Measure ratios if productive
  • Slip with and without different glazes.
  • In Glaze at different densities.
  • Slip as ink.
  • Slip wash then over.
  • Slip then coloured glaze.
  • Slip. Wipe off then different glazes on top.

Tile preparation

Azure Blue stain. Pot 1. Added 1/8tsp stain to 80ml slip. Mixed in with a short haired brush. Too weak. Added 1/8+1/4 then 3/4 then 1/4 tsp. Now have an intense blue slip.

Tile 24. Painted ‘as is’ down rhs. Then a second layer far rhs. Then watered next and finally very watered on final lhs strip and back.

Azure Blue Tile prep

Repeated for other stains:
Crimson. Pot 2. Tile 19. Mid was too weak.
Sun yellow. Pot 3. Tile 22
Autumn brown. Pot 4. Tile 18
Black. Pot 5. Tile 15.
Lime green. Pot 6. Tile 13.

Tile 14: yellow single coat base. RHS black wash. Lhs autumn brown wash. Then same for:
Tile 11: Azure Blue
Tile 3: crimson
Tile 2 Lime Green.

Black wash tiles 5, 12, 10
Autumn Brown wash tiles 1, 4, 9

Fired to bisque Programme 1.

Glaze choice

Selected this recipe from this article as a start point.

HIGH CALCIUM MATTE cone 6
20.00 Ferro 3195
29.00 Wollastonite
4.00 Nepheline Syenite
30.00 EPK China Clay
17.00 Silica

Note that this is originally from Mastering Cone 6 Glazes. An excellent book.

The article contains a number of other choices, but I prefer a semi-matt finish and the other options are glossy. We have also used this as a base previously, and so its should be a safe starting point.

Tile finish

Dipped once leaving a strip unglazed. Then dipped the top to get a double thickness. Fired the main coloured tiles, but not the wash-only one in this way. Fired to Glost Programme 2 on a plate – just in case. Some tiles, especially the early ones, were not sufficiently stable.

Also: May need to consider whether tiles need to be stackable in future.

Results

Unfortunately the kiln failed near the top temperature, and so didn’t fire down. Top temperature actually reached in unknown, but we suspect it was near top as the kiln was seen before failing at 1150. Programmed top is 1190, which equates to about 1220 with pyrometer to cone variation.

Crimson burnt out so was a vague pink. Top should have been 1140, so not too surprising. Red oxidation glazes and typically challenging. Same true for Autumn Brown, but not as bad.

Lumps of grog are coming through the the surface, so will need to sieve the larger grog out in future. Need an appropriate sieve.

Other ideas

Need to make more test tiles. Also picked up extra slips and brush on glazes from old stock for further experiments. Lastly, should I think the glaze, or maybe add CMC and “brush on”?

 

 

 

 

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