Do Glaze Materials Age?

[55Kevy]

I am a hobby potter who produced and sold enough work in the '70s to earn spending money.  I then graduated college in '77, entered the workforce and no longer had time for pottery.  In 2008 an overseas assignment looked like an opportunity to rekindle my interest so I purchased a wheel, an Olympic kiln, and a lot of glaze chemicals (feldspars, dolomite, flint, whiting, talc, various metal oxides, and the like) and took the lot to Indonesia.  Everything was stored in a shed that was air conditioned most of the time, but experience high humidity conditions not infrequently. In 2011 I repatriated to the US and the glaze materials were stored in ambient conditions in Bakersfield, CA.  In 2015 I retired and planned to restart my hobby in our retirement home.  

 

I am now finally mixing glazes for my first cone 10 reduction firing. I am mixing 4 glazes: a matte off-white, an Angelo Garzio recipe called Honey Brown, a celadon, and Shaner's Red.  Today when I mixed the celadon I found it to be quite gritty with what almost felt like sand, and I picked 2 hard grains of a white material (I haven't reviewed the raw materials to see what they likely are) that are about 5 mm in diameter.  My questions for the board are:

1. Is it possible that the physical characteristics of the raw materials have changed in the 10 years they've been stored in less than ideal conditions?  Are the materials I should throw out and repurchase?

2. Do I need to worry about loosing the small amount of material represented by the chunks described?

3. Should I quit mixing my own glazes and buy ready made?

 

Thanks in advance for your input.

 

Kevin Patterson

Novice potter in the SYV

[bciskepottery]

Can you provide the glaze recipe?  That would help determine if any materials could have changed.  Most materials are not affected by time, etc.  Others can be. 

[Mark C.]

1. Is it possible that the physical characteristics of the raw materials have changed in the 10 years they've been stored in less than ideal conditions?  Are the materials I should throw out and repurchase?

2. Do I need to worry about loosing the small amount of material represented by the chunks described?

3. Should I quit mixing my own glazes and buy ready made?

 

#1 most materials would not be bothered by any of this

#2 buy a thrift store blender and beat up the chunks-its easy and works really well-you strain them in a strainer add some glaze in blender within chunks blend for a few minutes

#3 NO -NO -NO you learned the right way and you should stay with that-store bought is just not the same.

[oldlady]

and some materials have been reformulated by the suppliers and your old stuff is possibly better than new.

[Denice]

A ball mill may be a good investment for you.  You can mill your raw materials and then have a nice piece of equipment for other uses.  If you decide to start over on your raw materials I am sure you can find a potter that will take them.  Potterbarter is a site online that potters sell, trade or give away pottery supplies. Denice

[Pres]

Mix the glazes, sieve twice, test. I have had materials that I have used for the last 15 years on the shelf in bags. Keep it dry, keep it up off ground, but moisture will get to places from the air. In the long run, I always sieve twice #80, and test. Most of the time I do get some gritty white material out, and I think I have read this comes from some feldspars or Nepheline Syenite, but it has not changed the glazes.

 

best,

Pres

[Magnolia Mud Research]

Some of the raw materials will become 'hydrated' after prolonged exposure to high humidity and will begin to 'cake' and become 'lumpy'. Carbonates are especially prone to this. 

 

Feldspars powders if wet for long periods can become "cemented" together by hydrates and carbonates when the water is evaporated.  The main problem to a glaze is the 'lumpy' effects on application and a longer time required for melting.  Crushing the lumps is not difficult  if the lumps are first separated from the fine powders.
    

Many of these materials can be dried by either calcining in a bisque firing (zinc oxide is one) or just heating to about 120-150 C for a an hour or so.  After calcining separate the lumps by sieving. 
  
I have learned to screen the dry ingredients with a flour sifter or putting them in a dry blender for a few minutes before weighing.

 

My motto is if you don't put lumps in the glaze slop you don't have to worry about getting them out.

 
lt

[55Kevy]

Thank-you all for your responses. In the middle of the night I remembered that I used to blend to get the lumps out, and that I have a screen.  So back to the drawing board for some of the work I inadvertently 'experimented' with yesterday.