Tuesday, September 8, 2015

New glazes mixed and ready to go on pots.

In a previous post, I explained how I first make 200 gram (about 2 cups liquid) trials to test glaze formulas on 3" x 4" clay tiles. From those I chose six to try out in a large enough batch to see how they perform on pots. If these new glazes perform well, I'll make 3 to 5 gallon batches so that I can dip larger pots and won't have to replenish the supply as often. 

A glaze that "performs well"

The glazes I make are called "dipping glazes" or "bucket glazes" because I dip the pots into the bucket of liquid glaze, or pour the glaze over parts of a pot to coat it. A good dipping glaze stays suspended, does not "hard pan" (settle into a very hard layer), coats the pot consistently, does not "drape" or make unsightly thick rivulets on the pots when they are pulled out of the liquid, and does not become too powdery to handle when dry. It often takes several trials to create a glaze that behaves well in the bucket, melts correctly, shrinks at a compatible rate with the clay, and looks great on the pots.

Glazing Set-up

Space is limited in my garage-studio, so I store the liquid glazes in food-grade lidded buckets on rolling carts that I can move out of the way when not in use. Small stainless latte pitchers with open handles are handy to hook over the rim of each bucket, ready for pouring glaze into the pots. 

Initially I use a power drill with a paint-mixing paddle to stir the glazes, and then put a long handled spoon in each bucket to give the glaze another stir right before I dip or pour, in case some of the heavier ingredients have settled. Another essential is a bucket of water and a small sponge to wipe glaze off the foot immediately after dipping. After the glaze has dried I do a final sponge cleaning with fresh water before each piece goes into the kiln.  


Monday, August 24, 2015

Another Kiln Load
Now that I have some new glazes, I'm ready to make lots more work and try out different color combinations. The textured handles add a tactile quality to the smooth mugs that enhances the experience of drinking a cup of tea or coffee. When I "pull" handles, I usually make one at a time and attach it right away to the cup, but when I hand-build handles I usually roll out a slab, texture it and then cut out all the handle shapes at once so that they look consistent. The picture shows some handles waiting on a damp cloth, and 2 already attached. The wonderful textured roller was made by my potter friend Angela Rogers. When they are completely dry, I begin stacking the kiln for the bisque-firing.

This week I also made some "curvy bowls" by throwing a rounded bowl and then cutting the curves and also holes for handles. Below is a bowl with pencil line guide for cutting. The 2nd picture is after the bowl is cut and edges are smoothed.

Monday, August 10, 2015

Kiln Firing Results, 

In this kiln I fired several sets of mugs to try out new glazes that I had tested in the previous firing. There are 5 to ten ingredients in a formula and each has a particular effect on the color, opacity and gloss, durablity, etc. Most glaze formulas are calculated to total 100 so that they can be compared. Sometimes I begin with a recipe/formula from a book and alter the ingredients to suit the pots I make. If the glaze will be used on my functional pots, I first enter the recipe in a glaze analysis program to see if the Silica and Alumina ratios are in the range of a stable glaze.

After I have tinkered around with the formulas, it's time to test my assumptions. I use a gram scale to weigh 200 grams total in each dry weight batch formula, which makes about 2 cups of liquid glaze. I mix each batch with water, screen, and apply to bisqued clay tiles, then fire to Seger cone 7 / 2230 F. with my own ramp schedule that includes controlled cooling, in a Skutt 10-27 electric kiln.  

before firing
after firing
My version of Xavier Jade
Mosley Olive Matte & White Liner
It often takes several trials to get the results I'm seeking. When I finally get a good test result I weigh out a 2000 gram batch to try on bowls or mugs in the next firing. These are mugs with my latest 2000 gram trials. I didn't expect so much blue in the overlap of Butterscotch over RR Black.

My version of Butterscotch with Ron Roy Black #3 Inside.

Sunday, August 9, 2015

Work ready for bisque

This first post is a record of recent work done in my home studio. 

I had access to both gas and electric kilns while I was a college ceramics teacher (since 1975) and over the years explored low, mid-range and high fire glazes, including raku, maiolica and salt-firing. At that time my focus with mid-range electric firings was making glazes that look similar to work fired in a cone 10 reduction kiln.

Recently I've decided to narrow my exploration to mid-range electric firings, exploring subtle glazes that will highlight my hand-built and wheel-made forms. I prefer to glossy glazes for the interior of functional pots, and mattes for their tactile quality on the exterior.  
Here are examples of some mugs, etc. ready for bisque firing. 
They will be glaze-fired to cone 7 in a computer-controlled electric kiln.