|
|
Post by erdergas on Jan 12, 2018 4:09:05 GMT -6
Hello folks, I'm having problems with this glaze on a flat surfaces, the glaze is beautiful on the outside of the pot and on the vertical inner surface, but on the inside flat part it's awful and looks under-fired, so far I've tried 2 things: Move further up with temp, but if I keep doing that I'll end up without crystals on vertical surface, it's already running a lot ) Putting less glaze on the flat surface ( The glaze from the border ran to the center anyway so I end up with the same mess ) Once the glaze from the border run to the center this is what I get:  Last idea: - Add more lithium on the glaze of the inner part, so it is more runny and the underfired cobalt and stuff can scape thru the hole on the center I'll appreciate so much your help, I'm a bit desperate, I don't know where to go right now. Thanks, |
|
|
|
Post by tileman2 on Jan 12, 2018 6:17:46 GMT -6
Eye of the beholder..problem.
I see it as too much lithium already. Several things can be done. 1. Mix enough for the outside, then mix another batch for the inside with 1/2 % less lithium. 2. Glaze the outside, then add 1/2% of alumina and glaze the inside and lower temp back down. Although you did not specify: the crystal formations strike me as cone 6. Cobalt likes to boil and run if too much lithium is added. If the glaze was less fluid you could get by with less cobalt and still achieve the same color: you are losing most of it at this point. I would also consider backing down the zinc as well: would help with the over- nucleation. Start with 1/2% reduction of zinc: and continue until you reach your artistic
expression.
Tom
Personally I would mix the recipe with 1/2% less lithium and zinc: and cut the cobalt back by at least a quarter. Glaze the outside, then add 1/2% of alumina and then glaze the inside. Some porcelain bodies have more alumina content than others: so glazes that would run on one, would run less on another.
|
|
|
|
Post by erdergas on Jan 12, 2018 6:47:32 GMT -6
Hi, First thanks for the kick answer and your time. Yes, it is cone 6, around 1255C, at 60 degrees / hour for the last 100 degrees. So you think the problem is that the glaze is to fluid because of the lithium and that makes the cobalt to boil, mhm, I'll try to reduce lithium/zinc on the inside and to add some alumina as you said, let's see what we get. If it helps, that's a picture from the outside part:  Many thanks  |
|
|
|
Post by mohawkpiper on Jan 12, 2018 13:34:50 GMT -6
added to that... it looks like you just dont have enough glaze on the bottom in the center.
G
|
|
paul
Junior Member
Posts: 51
|
Post by paul on Jan 12, 2018 14:00:13 GMT -6
Hi Edergas,
I think an easier solution is just make a better bowl / sink next time.
Make it with a rounder bowl shape, make sure you have some grade to the bowl, not flat on the bottom.
I Agree this one may need more glaze on the bottom.
Regards
Paul
|
|
|
|
Post by erdergas on Jan 12, 2018 14:34:21 GMT -6
It's not because of the shape, sure it could help to have it more rounded but the problem is on the glaze.
The aplication in this case was thin, but the one i tried before was thicker and the shape was more rounded, still, I had this blueish agregations on the middle, less than this time to be fair. So I thought it was underfired and I went 10 degrees C more up and with a thinner application, this did not solve the thing, and that is the reason why I'm asking.
My first thoughts were that was underfired and to thick, so I applied thinner and fired higher.
Later I thought about putting more lithium on the inner part of the bowl ( I've already have 4% of it on the glaze ), but as tileman2 suggested I'll try with less lithium (2% less) and less cobalt and 1% less of Zinc, and ¿thicker application maybe?
Really, thanks for your help
|
|
|
|
Post by bill2015 on Jan 13, 2018 16:13:02 GMT -6
I also fire at cone 6 and I posted this in a crystalline glaze FB group:
Using crystalline glazes on horizontal forms such as tiles, plates & bowls... One must adjust glaze application thickness, a thinner application than used on vertical forms. On flat forms a single layer, as opposed to 2-3 layers one might use on a vertical form. The glaze is generally not running anywhere and the glaze will produce crystals. With a horizontal curved form the glaze will run and "pool" in the center of the curve, so again, usually a single application layer is all that is necessary. I sometimes add a 2nd layer only at the rim as I know the glaze will run away from the rim.
I find the glazes that generally perform best by looking at what the glaze does in the catch plate of the fired vertical forms that had multiple layers of glaze applied. If the glaze that has run and pooled in the catch plate is glossy with no crystals, or very few crystals, I consider that glaze a good candidate for horizontal forms. If the glaze pooled in the catch plate is covered in 3D crystals with very rough surface, then that glaze will probably not work well on horizontal forms such as bowls.
Here's an example of a glaze that I used in the last firing that I had yet to test on a vertical form. I had more space in the kiln, so I test glazed on a bowl and the results were crap. Over nucleated and inside bottom covered in a rough textured surface, so it got the hammer. It split nicely down the center so i thought it would be a good illustration of how much glaze, even just a single layer application, runs and pools in bottom of a bowl form.
So it may well be a matter of selecting a different base glaze to use on forms with both vertical and horizontal area.
|
|
