What Has Gone Wrong With My Potters Choice Glazes?

[EmilyHalsey]

I have some test tiles that I recently had fired at cone 6. None of them look like they should. All but 2 or 3 are way too dark or are just the wrong color. Is it likely that they didn't fire hot enough? I did not do the firing and the guy who did does not have witness cones. The light sepia is almost a yellow color, the ironstone is a dark plum color, and the blue midnight is plain black. Does this seem like an underfiring issue or something else?

[Benzine]

Have you used these glazes, and specific bottles before?  Basically, is this a new issue?

 

Are you applying the recommended amount of coats?

 

Are you firing to the appropriate Cone?

[Pres]

Are they mixed well? Even commercials need to be well mixed.

[Chris Campbell]

If the person firing did not use witness cones then you have almost nothing to go on. When things get darker I think it hints at over firing but who knows??

Also ... Have you personally used those exact bottles of glaze before with success?

If not, then you have no useful information to make sure it does not happen again.

 

Make some test tiles, use those glazes alone and in combinations, take notes, buy some witness cones to give this person ... Maybe as a "thank you for firing my work" gift ... Then see what happens.

[EmilyHalsey]

I have never used these glazes before. They are in pint size containers, so I just stir them with a stick and shake them around before I use them. It's not that the glaze looks too thin or too thick. I applied 1 coat all over the test tiles, and then added a second coat 2/3 of of the way down after the first coat dried. Then did a third coat at the top once that dried. The thickness or thinness did not seem to be the issue. It was more that the colors had no variety whatsoever and looked very flat.

 

I told the guy to fire to cone 5 the first time. Those pieces looked like they had boils on them and looked awful. I gave him more tiles and told him to go to cone 6, thinking the first ones were severely underfired. The cone 6 ones have an even, slightly shiny look.

 

I will get some witness cones and hope that the temperature is the problem.

[Marcia Selsor]

are you using a dark clay body?

 

Marcia

[EmilyHalsey]

Speckled brownstone clay body

[Benzine]

What Cone does the bottle recommend, that you fire to?

 

The blistering at Cone 5, is from the glaze boiling.  It cooled, before those bubbles had a chance to smooth back out.  A hold at Cone 5, could potentially fix that problem.  But if you say the glazes aren't getting glossy until 6, may suggest another issue.

[EmilyHalsey]

It recommends cone 5-6. And okay I will try a hold and a longer cool down time. I am going to pay to use a local public kiln and fire myself so I can monitor and control everything. The tiles were still glossy in areas from the cone 5 firing, there were just also areas with hardly any glaze that were very matte.

[Benzine]

One coat, will most likely lead to a matte version of the glaze.  There isn't enough there to mature properly, and give it the glossy look.  If a glaze is really thin, sometimes, it won't even changed color, from its raw state.

[EmilyHalsey]

This effect happened even at the top of my test tiles where I had 3 coats. I will post pictures of all of this when I get to my computer in a couple of hours.

[Chris Campbell]

You have probably already visited this page but anyhow ...

 

http://www.amaco.com/learn-about-potters-choice-glazes/

 

Unfortunately it looks like most of the tests are on white clay bodies.

[Patsu]

I have some test tiles that I recently had fired at cone 6. None of them look like they should. All but 2 or 3 are way too dark or are just the wrong color. Is it likely that they didn't fire hot enough? I did not do the firing and the guy who did does not have witness cones. The light sepia is almost a yellow color, the ironstone is a dark plum color, and the blue midnight is plain black. Does this seem like an underfiring issue or something else?

Are you single-firing these at a fast glaze sort of ramp?  The carbon might not be burning out completely, were the tiles bisque already? Slow bisque helps to rule out carbon, as said before here 1100F to 1700F at 100/hr is good.  Potter's Choice are best applied in the coats specified individually for the glazes, a little hot is better.  Sounds like it didn't quite get there, but it's about the heat work over time which means you need to look at how long you are coming through the ranges and get the heat work done without rushing.  Try a few in again with a longer schedule maybe?  

[Marc McMillan]

there  is a thread about these glazes with lots of info. Most need a good thick coating. Also, I tend to have better success firing to c5 with about a 15 minute hold. 

[EmilyHalsey]

Here is a link to the cone 6 fired tiles: https://imageshack.com/i/p2ts9fNjp

 

The colors are blue rutile, blue midnight, indigo float, arctic blue, tourmaline, iron lustre, lustrous jade, chun plum, smokey merlot, ironstone, and light sepia.

 

I bisque fired to cone 04 before glazing these tiles. Someone else did the glaze firing for me so all I know is that they are cone 6. He probably was not very careful about the heating schedule and such since he is a sculpture and does not work with glaze.

 

For the next glaze test, I am going to use a public kiln and get witness cones. I will probably try cone 5 with a 15 minute hold. Thanks for the advice.

[Patsu]

Huh.  Here's an example of blue rutile from my stuff, cone ^5, maybe a 20 minute soak. Not the greatest example, blue rutile can really pop. See how I have interruption to the translucency that I'm not seeing in your test pieces as you are saying.  This is on porcelain.  You gotta really grub down into the bottom of those containers to break it up, could be you skimmed over the bottom without getting through it?  & stir a lot.  Not sure.

[Roberta12]

Emily, this much I do know.....I get different results on different clays.  I have a pallet of glazes that I use on the speckled buff clay.  But not all glazes work that well on that clay.  I have recently been working with a red clay (sb red) and same thing....I have a few glazes that are spectacular on that clay.  But not all.   If I really want nice bright colors I use a white clay body.   Maybe that is the difference?? 

 

Roberta