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effect of altitude on firing

updated mon 31 mar 97

 

boutique@island.net on tue 25 mar 97

Hopefully somone has a better sense of what altitude/barometric
pressure does to a firing than I do. We have been firing decals,
and having some different results, particularly with the reds. Now I
realize how difficult red can be in glaze and the decals are using a
ceramic ink, but, shouldn't the firing results within the same kiln
load be the same?

We can see a range anywhere from the red/burgandy that is desired, to
strong red, mauve and light purple. We have been told by the
manufacture that they can fire from 1300 - 1450 F and he claims to
have test fired to 1500 with the colours staying true. We are now
fireing to cone 018 and having better results, but still not where we
would like to be.

We are located at sea level on the West Coast and the manufacturer is
in Toronto (356 feet). Granted it is a bit higher, but will this account for
this range of colours?

Has anyone experienced this problem, or have a sense of how to solve
it?

Thanks for any insights that you may have.

Ken Ford on wed 26 mar 97

I dont know about altitude difference , but have been into decals for some
time. When there is variation like you describe there may be some reduction
occuring that your reds are very sensitive to. This may be caused by the
medium and cover coat burning out, especially if fired quickly. Its good to
take at least 3 hours to cone 018 at a steady rate. If possible with the
door open or at least all bungs out.
Good luck , Ken Ford