Wood Ash Proportion As An Addition To An Existing Glaze

[PottaFella]

A few queries to help with new glaze.

 

I'm in process of making up a wood ash glaze - my first.

 

I have collected a quantity of Birch wood ash, I've soaked it and sieved it through a fairly fine stainless (kitchen sieve) mesh, the result is a slop which contains ash particles up to the size of fine sand/caster sugar.

 

I hope to add some of this to an existing attractive blue/grey alumina matt glaze to give more interest – perhaps some 'toasty' edges or speckling within the fired glaze and a degree more translucency.

 

I will do some tests quite soon, but can anyone maybe tell me if I'm in the right area to get something interesting?

 

My alumina matt glaze is:

 

Soda Feldspar 70

China clay 13

Dolomite 5

Whiting 5

Quartz 3

 

• The ash seems to settle out extremely quickly, I guess this will improve once other ingredients are added?

 

• Should I sieve the wood ash to exclude all but the finest particles?

 

• I think the ash glaze is more of a flux? so if I add some to the recipe above it should make it more glassy/runny – is that correct?

 

• I'm thinking to try test adding between 10% and perhaps 30% of the ash glaze (this is just a guess – perhaps I should use much less or more)?

 

• My normal colouring for the alumina glaze is either small amounts of cobalt/nickel to achieve a subtle blue grey or titanium/rutile to achieve creamy white – is it possible to predict what the addition of the Birch ash will do to these colours? Are they likely to change substantially?

 

Very many thanks for any help in predicting what may happen/what I might expect!

 

 

[rayaldridge]

This is one of those "you have to test" situations. 

 

You'll also have to dry the ash before you test it in your glaze, so your weights will be easily measurable.  If I were you, I'd start with 10% and then go up from there.  Put your test tiles on pads of unglazed clay or slices of insulating firebrick, because ash glazes run a lot.

 

Your glaze already has a fair amount of calcium, and this is the element that makes ash glazes act like ash glazes.  Calcium can have a bleaching effect on some colorants if used in the amounts commonly found in ash glazes.

 

Let us know how it goes.

[jrgpots]

When your ash is still wet, make pellets by compressingsome of the ash in a straw, then allow the pellets to dry.  Once dried put the pellets in a catch basin in the kiln during a glaze firing.  This should give you a good idea of what the ash will do (especially color) before adding to a glaze.

 

Jed