Disappearing Glaze

[Babs]

From that pic. The glaze looks too thin even initially.

Time to test the Specific gravity of glaze if need to reproduce effect.

Great link by Min here re how to do that.

Some glazes can handle water beung emoved from top of bucket after it has been allowed to settle a while thus giving you a thicker glaze.

Forget glaze vanishing into the ether.

Don't reach thosetemps in your kiln:-)

Neil's method is a good one as it works for his glazes but as he gets on to say some glazes wont handle drying to that extent.

Change one thing at a time she says.

[Malcolm]

I know you’re right and I will check the Specific Gravity of my glazes. I thought it was OK to run excess water from a bucket before stirring and always have done so but I now know certain ingredients can dissolve in water and I would be running those off. It’s very hot weather here and I can put my glaze buckets in the sun and get the water to evaporate off.
I didn’t see a link and so I don’t know who Min or Neil are.

[Babs]

@Malcolm

Min is a moderator of this forum.

Neilestrick is moderator of Equipment Repair forum.

If hot and humidity low, shouldn't need to leave overnight but just till you get result you need:-/

Specific gravity 

Check out John Britt  specific gravity of glazes on youtube.

Or search in these forums.

@Min is a great help with this

[Min]

@Malcolm, everyone has covered what I think is going on with your glaze already so I won't rehash what has been said about glaze application.

What I would suggest is to start measuring the specific gravity of your glazes. Doing this will rule out one of the variables you have going on (ie glaze density / thickness). You need an accurate scale plus either a large syringe or a beaker shaped cup or a graduated cylinder. Basically what you are doing is comparing the weight of the wet glaze to that of water. John Britt video below showing how to do this, relevant part starts at the 3 minute mark. Another link here about specific gravity of glazes. (I find the large syringe method the quickest) Once you have the glaze working as it should then each time you go to use the glaze do a quick check of the specific gravity. You might find that over time the specific gravity increases as water is drawn off into the bisque or through evaporation. If you are using a dry glaze then checking you haven't added too much water is a good idea also. I'ld suggest if this is the case then mix the dry glaze with less water than the commercial glaze instructions give, measure the specific gravity and then top up the water only if necessary. You might find you need less water than what is called for. There is no one magic number for what specific gravity you need, each glaze type is going to be different dependant on glaze materials used. When you have the glaze working as you want it to then note the specific gravity for that glaze on the bucket and in your notes.

I'ld also suggest taking some test tiles made from the same clay which are approx the same thickness as your pots and dipping once all over the tile, then half the tile with a second dip then dip one corner of the tile with a third layer of glaze. Wait until the wet shine is off the glaze before doing subsequent dips. Make 2 sets of tiles for each glaze, with one tile wait until the glaze is dry then scratch through the glaze but don't fire it. You want to be able to see how thick the dry glaze is. Fire the second test tile and compare results of raw unfired glaze thickness to fired tile. I'ld also do some small test cylinders, again make them approx the same wall thickness as your pots. Glaze the inside on one followed by the outside as soon as the liner glaze is dry to the touch. For the other cylinder glaze the inside then leave it overnight to dry then glaze the outside, fire and compare the results.

 

 

 

[Malcolm]

Thanks for the replies Babs and Min. The John Britt video is excellent. I will watch his whole series. I need to get some equipment then do some rigorous testing.

[Babs]

 holding the length of time you dip for is also important...