Help with white cone 6 glaze

[ACP]

Hi guys, I bought a commercial white cone six glaze that is super standard and widely used in New Zealand. However, instead of being opaque as it should be, it comes out looking translucent, sort of milky. The glaze is mixed to average thickness and I coat for about five seconds. 

I also  bought the brush-on version of the glaze but that comes out the same way. With the brushable glaze I apply three coats. 

I then fire to cone 6. My kiln sometimes overfires to about cone 7. Could this be the issue?  

A photo is attached with the glaze on two different clays. On the tile on the right, the glaze can be seen on the lower half. 

Any help would be much appreciated!

[Hulk]

Hi ACP

The glaze looks nice to me. On the buff clay, right lower, is there a fine crazed pattern, or tiny bubbles? Just curious, looks like something reflecting light in the glaze. 
Looks like the red blush and the glaze have healed over to a nice smooth finish, however, close inspection under good light might show otherwise.

Is the glaze more opaque over other clays?

It doesn't have much color to it though, no. My just a hint of white liner glaze uses zircopax, softer hint of white low sheen glaze uses tin oxide. A bit more of these opacifying ingredients - more color, more opaque!

I want to ask that you've really mixed the glaze well, really well, and again right before each use - just to cross that off, else.

[Babs]

Ring the supplier. And send the photos.

X2 Hulk, stir well. Higher temp should not affect tin or zircopac  opacity, but causes some glazes to thin as it moves more and so opacity may be lost a bit.

[ACP]

1 hour ago, Babs said:

Ring the supplier. And send the photos.

X2 Hulk, stir well. Higher temp should not affect tin or zircopac  opacity, but causes some glazes to thin as it moves more and so opacity may be lost a bit.

Thank you Babs! I actually contacted the supplier the first time I had the issue and they sent me a new packet of glaze. However, that has produced the same results. I then tried the brush on - same thing. This leaves me to think I'd doing something wrong. Maybe it needs to be applied much thicker, but it's quite thick already... 

[ACP]

9 hours ago, Hulk said:

Hi ACP

The glaze looks nice to me. On the buff clay, right lower, is there a fine crazed pattern, or tiny bubbles? Just curious, looks like something reflecting light in the glaze. 
Looks like the red blush and the glaze have healed over to a nice smooth finish, however, close inspection under good light might show otherwise.

Is the glaze more opaque over other clays?

It doesn't have much color to it though, no. My just a hint of white liner glaze uses zircopax, softer hint of white low sheen glaze uses tin oxide. A bit more of these opacifying ingredients - more color, more opaque!

I want to ask that you've really mixed the glaze well, really well, and again right before each use - just to cross that off, else.

Hi Hulk, no crazing on the tiles. The glaze has the same transparency on all clays. I could try more opacifier - would be a guessing game on commercial glazes as I don't know what they're made of. I think I need to make my own! I'm wondering if the application is thick enough it's pretty thick but I might try even thicker. 

[Min]

Is this a glaze recipe your supplier mixes in house? Is there a batch number?  

[Callie Beller Diesel]

The things that will make a glaze white don’t usually burn out at all, so I don’t think it’s your firing doing this. 

My inclination is that it’s an application issue, and you just don’t have enough on there. Average thickness could mean a lot of things, and a 5 second dip in a glaze with too much water could still result in a thin application. Looking at the buff test tile, it looks like the coral coloured glaze is also on the translucent side.

Does the supplier have mixing instructions that recommend a specific gravity measurement, or tell you how much water to add to dry ingredients?

[Pres]

Were these test tiles fired with anything else?

 

best,

Pres

[Chilly]

Try firing some more test tiles. 

1 with your normal timed application, 1 with 7 seconds, 1 with 10 seconds. 

Another set with one 5 second coat, followed by a second 5 second coat, etc.

Repeat with the brush on glaze, 1 coat, 2 coats, 3 coats, 4 coats - each applied in a different direction.

Make sure all tests are on cookies in case they run onto your shelves.

This is something I do with all newbies to the community centre, as we all have a different version of 3 flowing coats!

[ACP]

10 hours ago, Chilly said:

Try firing some more test tiles. 

1 with your normal timed application, 1 with 7 seconds, 1 with 10 seconds. 

Another set with one 5 second coat, followed by a second 5 second coat, etc.

Repeat with the brush on glaze, 1 coat, 2 coats, 3 coats, 4 coats - each applied in a different direction.

Make sure all tests are on cookies in case they run onto your shelves.

This is something I do with all newbies to the community centre, as we all have a different version of 3 flowing coats!

Thanks very much Chilly, I'll give it a go. The buff tile is 3 coats brushed on, so will have to start with that as the minimum for the brush on. Appreciate your advice!

[ACP]

22 hours ago, Pres said:

Were these test tiles fired with anything else?

 

best,

Pres

Hi Pres, yes they were fired with other pieces and in two separate firings. The other glazes came out as expected. 

Many thanks,

Anna

[ACP]

On 4/12/2022 at 6:07 AM, Callie Beller Diesel said:

The things that will make a glaze white don’t usually burn out at all, so I don’t think it’s your firing doing this. 

My inclination is that it’s an application issue, and you just don’t have enough on there. Average thickness could mean a lot of things, and a 5 second dip in a glaze with too much water could still result in a thin application. Looking at the buff test tile, it looks like the coral coloured glaze is also on the translucent side.

Does the supplier have mixing instructions that recommend a specific gravity measurement, or tell you how much water to add to dry ingredients?

They just have generic instructions for all glazes. This one should be applied thick. I thought I had mixed it thick enough but probably not. I'll wait for it to settle and remove some of the water, then try again. Someone else has also suggested increasing the dipping time. It definitely sounds like an application issue so I'll test some more. Many thanks for your advice!

[ACP]

On 4/11/2022 at 2:20 PM, Min said:

Is this a glaze recipe your supplier mixes in house? Is there a batch number?  

I don't think it's an issue with the glaze itself (supplied in powder form). The first time I bought it and got these results, I wrote to them and they sent me a replacement. I got the same results so I think it's something I'm doing. The fact that I get the same issue with the brush on glaze which is purchased separately further confirms this. 

[Pres]

@ACPDid any of the other pieces have chromium in the glaze?

 

best,

Pres

[ACP]

51 minutes ago, Pres said:

@ACPDid any of the other pieces have chromium in the glaze?

 

best,

Pres

Sorry Pres, I don't know - they are all commercial mixes. I'm doing a course with Matt Katz at the moment on glazes so hopefully will be mixing my own in the near future, but for now I'm just relying on store-bought. 

[Pres]

Just a weird thought, but years ago I had a problem with a base glaze that used tin, the glaze would seem to flash pink whenever there was a chromium green glaze in the kiln. Probably not that problem, just a thought.

 

best,

Pres

[Callie Beller Diesel]

18 hours ago, ACP said:

I'll wait for it to settle and remove some of the water,

If the water layer on top of the glaze is discoloured at all, this is not advisable.  Some glaze materials are soluble in the bucket, and you can mess up your chemistry if you discard it. If you’ve got time to leave the lid off the bucket for a few days, that’s a better method. Or, you could also consider adding some more dry glaze to the batch. 

As something for your own records, a good thing to do is when you’re testing this glaze again is to measure out 100 ml of your thoroughly mixed glaze into a clean and dry container, and weigh it. Divide the resulting number by 100, and that’s your glaze’s specific gravity. Some glazes are more sensitive to this number than others, but knowing if there’s a range you need to stay within to get the results you desire will help you get those results consistently. Specific gravity is very much a “to taste” measurement. The “right” one is subjective and very dependant on a lot of moving parts. You won’t usually find more than suggestions in glaze books or with some commercial dry mixes. 

As a very broad generalization and assuming there’s no ingredients that affect a glaze’s flow, an SG of 1.35 would be a very watery glaze, and something as high as 1.6 or 1.7 would be like a slip. Mostly you’ll see people recommend something in the range of 1.45-1.5, but again, that depends on a lot on your materials, your clay, your firing, and how you prefer the glaze to look.

You’ll see recommendations for lots of different measuring devices to use, from a clear plastic cup you calibrate on your own scale, to a graduated cylinder, Many of us here find it easiest to do with a 50 ml syringe, and just double the weight before you divide by 100. You can get them at some pharmacies that handle some medical supplies, or your vet, or The Online Store That Shall Not be Named. 

[neilestrick]

I'm wondering if they forgot to add the opacifier. Even thin, a white glaze should show some signs of whiteness, and this has none.

[Min]

2 hours ago, neilestrick said:

I'm wondering if they forgot to add the opacifier. Even thin, a white glaze should show some signs of whiteness, and this has none.

That’s what I wondered too and why I had asked about batch numbers.

Dry mix split into brushing and dry mix base without the opacifier.