Logan Oplinger on thu 22 feb 01
Lorri in Kansas,
Sorry if this is getting to you a bit late in the posting, if so, just delete.
>From your writting, you may be misunderstanding the term vitreous, which means to be "glass like" or non-porous. If the clay were vitreous, you would not have a problem w/ oil seepage. Yes, try firing to cone 7, but check with the supplier of your clay first to determine firing range. Also, do porosity tests as have been described in detail elsewhere in Clayart archives and in pottery texts. Your glaze may also be a problem, as it may be crazing/crackling - producing fine cracks - which allows oil to seep through into and through the porous clay. Start by finding a good base glaze which does not craze, one which fits the clay body at the cone you are firing to. Again, check the archives. A last suggestion, you may, I say 'may' be able to find a sealer which will not be affected by the oil in the lamps if you do not want to change the formulation of you glaze for some reason.
---- you wrote:
....It could be that these oil lamps I have made are cone 6 and
> perhaps I should try them with cone 10 instead and get better results.
> Perhaps a factor, perhaps has nothing to do with the problem. Another
> thought is that the clay is still somewhat vitreous so firing to cone 7
> instead of 6 might take care of the problem. But again, if it is a cone 6
> clay, that might not prove to be such a good idea. BTW, I glazed inside and
> out with the base of the lamp glazed as well to try to ensure it was well
> sealed. Any ideas what causes this to happen and how to prevent it?
> Welcoming any thoughts,
> Lenexa, KS
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