Wednesday, 1 October 2014

Post 174 Glaze Trial number 9

I've been making a few pots lately and have a kiln load full and few more drying. While they are I've got onto another trial of glazes. Frankly I've been putting this off for some time and every time I think about it again I change my ideas a little on what to trial. Perhaps that's why it hasn't happened - just hadn't reached that point of commitment. Or mabee it's just that it's such a tedious task. Oh yes and the fact that keeper recipes are in the minority.

In my first posts on glaze testing back at Post 30 and Post 32 I provided the recipes for a number of the base glazes I use.
At Post 77 and Post 79 I covered some work on brown glazes. That was trial 7 and I see then that I missed posting anything on trial 8.

It all starts on the computer with recipes expressed in percentages which then have to be converted into actual weights to mix. I'm now doing individual glazes in 15 gram batches for trial so the percentages have to be converted to add up to 15 grams, without missing any components. Then you have to get down and do the weighing out.


I have a number of base glazes which I use and within each a number of favoured glazes. The objective of this trial is to take those favoured glazes and make minor variations to the recipes to create a number of ranges in tone. So that has made the preparation a little easier. For example if I have 6 glazes to be made from the same base I then mix up 6 * 15 grams of the base and then divide the mixed base between 6 containers for the colourants to be added. That takes a little precision but can be done accurately with a well calibrated 50ml plastic syringe.
On top of that plan there were a few other individual recipes that I wanted to try, as well as a number of overlays combinations.

As you can see from the cup array above I use small disposable 200ml plastic cups to mix and track the trial glazes.

 After all the precision weighing, mixing and combining comes the painting. Because I paint the glaze onto my pots I don't dip or pour to glaze the test tiles, so I paint the test tiles. You begin to see why it is quite a task. This trial came to 53 tiles and I know I can fit 60 in my little kiln.
In this shot you can also see my formulation spreadsheet. The only way I can keep track of what I'm doing as I weigh out is to cross off the material at each recipe. You can see on the spreadsheet the number of individual weighings this trial has taken, by the number of crossed out components.

 And here they are loaded in my little kiln. I've tracked the actual firing performance I use in my big kiln - which is just a little different from the controller schedule because the hotter it gets it is less able to maintain the same rising temperature rate. So the little kiln is programmed to replicate the actual firing achieved in the big one - a very important step for a trial using a different kiln.
Fingers crossed - let's hope more than a few will be keepers.

A couple of days later now and I've edited back into the same post. Here is the first shot of the result, whcih produced some very useful variations. More detail to come.

No comments:

Post a Comment

Happy to hear your advice, feedback or questions