mid range clay, 04 bisque, LUG & glaze - what should glaze firing temp be?

[Jcarey]

mid range clay, cone 04 bisque, applied LUG underglaze and clear glaze - can glaze fire be to cone 05 or do I need to fire to cone 5?

[Callie Beller Diesel]

That will depend on the glaze you put on it. If you're using a commercial product, the specs should be on the product.

If you're making functional items, it's best to use a glaze that matches the temperature that the clay matures at, in your case cone 5-6. If you glaze mid fire clay with a low fire glaze, the clear is unlikely to fit well. If the glaze crazes over an underfired clay, it's going to seep. If the piece is sculptural, don't worry about it.

If you're worried about your underglazes burning out, I find most of them will hold up to mid-fire temperatures without altering too much. 

[Jcarey]

First glaze firing for me:)  

The glaze is amaco LG-10 clear.  Product specs say cone 05.  Clay is mid range Great Lakes supply Buff with range 4-10.  Pieces are vases, bowls and some jewelry.  Underglazes and bisque to 04.  Glaze application - some pieces were dipped, most brushed, all have 1/4" of no glaze around bottom.

So... should this be fired to cone 05 to match glaze or cone 5 to match clay?  I have heard from someone that LG-10 can be fired higher.  I was thinking of glaze firing to cone 04 just to be safe but then wonder what that means for the clay.  the bisque turned out fine at cone 04.

thanks for replying.  I want to have fire over the weekend for Mother's Day:)

[Denice]

You need to do some research on clay, glazes and firing,  you can end up with a real mess in your kiln.    Find a clay that has a short firing range like 5/6,  you usually need to fire a clay  that is  C6/10 too  C10 to get it to vitrify.  You can make  nonfunctional  items with it and fire it to C5,  but buy new clay for your mugs,  bowls and vases.   Unless your work is vitrify it will break easily and soak up water like a sponge,  what cone does your underglaze fire too?   Ask the store you got your glaze from if it can be fired to C5 or look it up on the internet.  You don't want the clear glaze to melt all over your shelves.   I have seen many kilns that have been damaged from glaze running amok,  if the owner had  just read a book on clay and glazes.    Denice

[Callie Beller Diesel]

@Jcarey If you fire a glaze that’s rated for 05 to cone 5, it’s going to run straight off the pot, which is no good for either kiln shelves, or for staying in your studio’s good graces!  Some glazes can be pushed a cone or 2, but not by quite the amount you’re proposing. And as mentioned before, the functional pieces will seep if the clay isn’t mature.

You could still be in luck though, because you’ve mentioned that the underglaze is already bisqued on. Just rinse the cone 05 glaze off and allow your pieces to dry at least 24 hours before re-glazing. Go back to your supplier and ask for a clear that will fire to cone 5 or 6, and glaze with that instead. 

With a cone 5-6 clear, you’ll find you want a thinner application, or they can go cloudy. 

Hope this helps, and keep going.  You’re asking good questions, and ceramics has a pronounced learning curve. . 

[Sheree]

anyone.know if i can glaze a 5 glaze over a low fired bisqued clay body?

will the clay melt if it has already been fired once? 

[Hulk]

Hi Sheree!

Low fire clay will likely slump/melt when fired many cones over its rated maturity temp. Match glaze and clay!