Milky 'Clear glaze' - (again!)

[ValK]

If feldspar gets damp. could it affect the resulting fired 'clear' glaze = milky?

[Callie Beller Diesel]

Hi and welcome to the forum!

To answer your question, no, damp feldspar will not make a glaze milky. If you’re using it as a glaze, it’s in water anyways.

If your clear is milky, there’s a few things that could be going on, the most likely one being that it was applied too thickly. If you give us a few more details about the clay and glaze you’ve used, the firing cycle if possible, and how you prepared and applied the glaze, we can better  help narrow down what went wrong.

[Bill Kielb]

An example picture or two would likely help as well.

[ValK]

Thank you for the welcome, and prompt response.     The bowls are white stoneware with 10% silver sand addition, to aid wide throwing.  Clear glaze recipe is one I have used for some years.  But was not tested brfore application! schoolgirl error!  As (I believe) I was meticulous in the measuring and sieving, I thought the damp feldspar could have affected the ratio of materials.  Glaze was poured over underglazed, bisque fired work. - (maybe too thick? ) Fired to 1260'C.   Rate: 150' rate to 300', 5 min soak,  130' rate to 1260' , 5 min. soak.

The image is after glass inlay applied and a second firing at the same rates.  

[Callie Beller Diesel]

Hmmm.It doesn’t sound like the mixing would be the problem at all, so that ‘s good. I don’t know that it’s your application either, because it seems pretty well melted and I don’t see any drips or runs.

If the feldspar had somehow gotten water into the storage container and the material was damp that way, it’s possible for the chemistry to have been be affected. If this was what happened, it would be easy enough to rescue the material by laying it out on a cookie sheet to dry. If you needed to accelerate the process, you could put it in a low oven or kiln set to hold at 80 C. But if you live in a humid area and all your other materials were similarly damp just from the atmosphere, it might not have been a significant factor.

If you’d be willing to share it, the glaze recipe would be most helpful.

That looks more like boron clouding, or some other kind of phase separation that more frequently happens when there’s some form of titanium present. If you’re sure you’ve measured the glaze out meticulously, that leaves possible titanium somewhere in the clay. You mentioned adding silver sand to your clay body. Did you get it from the landscape nursery, or from your pottery supplier? A brand name so we could maybe try and check the composition on it is another line of thought.

 

[Min]

8 hours ago, ValK said:

The image is after glass inlay applied and a second firing at the same rates.  

I know this wasn't what your post is about but....

Very risky to fire glass on ceramics, it's not something many here would recommend doing for safety reasons. Link below to a thread discussing why.

https://community.ceramicartsdaily.org/topic/19438-firing-glass-on-clay/

 

[Bill Kielb]

9 hours ago, ValK said:

was meticulous in the measuring and sieving, I thought the damp feldspar could have affected the ratio of materials. 

If it was damp, then yes it would have affected the weight of materials as you mixed. In theory the damp feldspar would have been heavier than dry so again in theory you would likely add less than the recipe called for. Changing the chemistry of the recipe definitely could have any number of affects.