Raku pot liner question

[JohnnyK]

I've been thinking about Raku firing again and was thinking that I would fire my ^10 Raku clay with a ^6 liner glaze on the inside to seal it and then do the normal Raku firing. Has anyone done this before and did it work to seal the pot or vase from leaking if filled with water?

[Callie Beller Diesel]

You’re not the first person to have that thought, but I’ve never seen anyone bring it into common practice. Your best bet may be a non-fired sealant of some kind. 

Keep in mind there’s a lot of folks that come to this forum looking for help troubleshooting a cone 6 glaze they’ve put on a cone 10 clay body. If the glaze winds up crazed and the body isn’t mature, it’ll weep. 

[Rae Reich]

It would have to be a liner glaze that is able to deal with the thermal shock of rapid temp changes - haven’t found one yet. 
(I would use FlexSeal after firing)
Good luck!

[neilestrick]

Chances are the clay will be too tight after cone 6 to survive the shock of raku firing afterward. It will also be too tight to carbon trap the way it normally would in raku. And the liner glaze would likely craze from the thermal shock, in which case you'd still have a leaky pot since the clay wouldn't be fired to maturity. And applying the raku glazes will be a bear since the pot won't be absorbent after cone 6. Unfortunately you just have to accept raku for what it is- not water tight.

[PeterH]

IMHO the problems of thermal shock make this a highly "challenging" project. Not least because you will presumably be "guaranteeing" your customers that is safe to put these vases on top of their cherished woodwork.  However a couple of observations.

What sort of raku finishes were you thinking of using? Presumably the "crackle" ones demand a certain amount of thermal shock to start the crackle before smoking, while any thermal shock involve in "reduction"  is incidental and not necessary for the final effect. Indeed thermal shock of reduction pieces might be minimised by firing them in an (open-topped?) saggar, which could be taken out of the kiln and reduction materials added to the saggar.

OTOH the crackle finishes might stand up better the the ware-and-tear (and wetting) a vase is subject to.

I assume a liner glaze on the inside of a pot would be less subject to thermal shock than the outside of the pot.

I'll just mention an oddity that the raku artist Tim Andrews produced.

The glaze was a mid-fire crackle, which he fired and cooled as normal. He then re-fired/warmed the pot before taking it from the kiln and covering it with sawdust. Minimising the 2nd firing temperature, and presumably thermal shock, involved in smoking the already crackled pot.