Wednesday, October 22, 2008

Mixing Glazes for Brushing

One thing that crystalline potters must be aware of is that certain crystalline glazes do not store well. If they are zinc oxide based, they could develop actual crystals in the wet glaze in just a couple of weeks. These crystals change the formula of the glaze and make it not so good.

So it's prudent to not mix up too much glaze, especially if you are working alone or in a small studio. When you are only mixing up enough glaze to apply to the pots immediately, the problem of how to apply the glaze comes up. Basically it comes down to whether you want to brush or spray your glaze. For many reasons, I decided to brush the glazes on my pots.

So what is the best way to prepare that glaze for brushing? It's pretty complicated but I'll try to explain it here and also let you know that I am still tweaking the process. Here is how I mix up 300 grams of glaze, my normal amount. 

Be sure to wear a mask and rubber gloves. You can get the purple ones at Sam's Club for cheap and just throw them away every time. 

Add the dry glaze ingredients to a one quart yogurt container. Be sure to have a check off system so that you don't make a mistake. I always make a check mark on my glaze mixing notes when the yogurt container that I am using to weigh the chemicals is on top of the yogurt container that is holding the glaze. That way I know what I have done and the materials have a chance to settle a little. It's good to have a slight breeze away from you too. 

When you have all the ingredients in the container take a dry heavy duty plastic fork and stir them until they are homogeneous. You don't have to go overboard here, just make sure you don't have large clumps of single materials. 

Add a measured amount of pure water. Don't use tap water as it will change over time. I usually add between 250 and 300 ml of water to the glaze, but this will depend on how you like your glaze. All I am saying is that water is one of your glaze ingredients and you want to know how much you are using so that when you get it right, you can add that amount each time.

Allow the glaze to sit for a few minutes so that the water can penetrate the dry ingredients.

Add about 3 tsps of CMC solution. 

When I mix CMC I put hot water in a blender and add CMC powder until I can't add any more -- the powder is not going into solution. I let it blend for a minute or so and then pour it into yogurt containers and let it set for a couple of days until the clumps dissolve. My solution is kind of thick -- not real thick like honey but sort of thick like maple syrup. 

Mix the glaze with a hand blender until you have dissolved all the clumps and it is ready to pour.

Pour it through a 100 mesh sieve and then back through the sieve into the original container, which has been washed out so that no granular stuff is still there. So you sieve it twice. 

At this point your glaze should feel somewhat watery because you have deflocculated it with CMC. You don't want to leave it like this or it will settle.

Bentone EW is a suspender that works much better than Bentonite or V-gum-T or Macaloid. I got some years ago from a paint chemist and I do not know where to get it now. I'm still playing around with the amount to add to the glaze but today I added one gram of Bentone EW to  300 grams of glaze and it thickened it and suspended it a lot. After adding the Bentone EW you have to blend it into the glaze and let it sit for at least a half an hour.

If the glaze seems perfect then you are done. But I usually add a few drops of Calcium Nitrate solution to help with the fluidity of the glaze. You will again want to use the hand blender (I just got three of them on sale at Macy's for 19.99 each).

If you get the right amount of Bentone EW you don't need the Calcium Nitrate solution. 

At this point, your glaze should be ready to brush. You may have to adjust the water so that the glaze is to your liking. 

Mixing Calcium Nitrate:

Add 5 pounds of Calcium Nitrate pellets to a gallon of water and blunge until the pellets are in solution. There is all this crap in the mixture and you have to get it out somehow. Some you can get off the top and some you will have to wait until it settles and then take the clear off the top. It will take you a few days until your solution is totally clear. You just keep decanting the clear. I have tried pouring it through coffee filters but even the very fine stuff  -- probably EPK -- goes through. 

1 comment:

EF said...

Thanks for the hot-tip!