Week Two

Week Two

The sun blazes down relentlessly as I lug two buckets of dam water out into the paddock to water some of Paul's fruit trees.  He has quite an orchard of sub-tropical fruit trees, many of which are mature, and makes jams and jellies himself.  But they require quite a bit of TLC during hot Summers.  Watering the trees and the grape vines is part of my job list and I don't mind at all, since I love to garden.  He has a vege garden and a water feature that also require weekly watering.  

After the watering, I meticulously sweep everywhere and dust all the pottery pieces in the gallery.  Again, I don't mind since I am committed to giving one whole day to maintenance around the workshops.  Today, the boss was talking about teaching me more of the business than just the pottery making.

This week there were several highlights...

Next to the gas kiln area is an old cold room which has been turned into a drying shed.  Here we store  drying greenware, and bisqueware awaiting a glaze firing.  There are two types of firing: reduction and oxidation.  As I understand it, an oxidation firing draws oxygen into the kiln and this reacts with carbons in the clay.  

"When heated sufficiently, many substances oxidize if there is free oxygen available. Volatile portions of compounds and molecules break free and the free oxygen then can attach to the remaining material, forming oxides. This process is called oxidation." Peterson (2016)  Peterson goes on to explain that many metal compounds revert to their oxide forms in this firing.  For example, copper carbonate will burn off its carbon and attach free oxygen, forming copper oxide.

In reduction firing, oxygen supply is reduced inside the kiln.  This makes the carbon in the clay rob the oxygen present in the clay and glazes, often having a dramatic effect and changing the colours of the glaze.  An example would be the copper glazes; they turn out green in an oxidation atmosphere and red in a reduction kiln.

  

Digitalfire.com (2003) notes that "Copper normally produces green colors in amounts to 5% where it moves toward black.(In reduction firing, it turns to Cu2O and gives vibrant red hues)."  

I had a basic idea about the differences between these two firings but it is good to read about it.

In the drying shed, I learnt that it is ok to stack greenware ready for its first low firing (bisque).  There is a certain way of stacking to save space in the kiln.  Space is of a premium because it costs money to fire the kiln.

After that, I learnt to trim the bases of some pots.  I trimmed many bases of work done by other students.  It was nerve wracking at first, but became easier as I grew confident with the tools.  I found out why it is important to keep a hand on the top of a vessel if its sides are quite rounded - it literally flies off the wheel!  It was rather like turning wood on a lathe.  You have to hold your hand very steady and watch the profile of the piece as it's spinning furiously.  After a while, it is pretty enjoyable!

Peterson, B. (2016). Oxidation and Reduction Atmospheres. Retrieved from https://www.thespruce.com/oxidation-and-reduction-atmospheres-2745940

Digitalfire.com (2003). Copper Oxide Black.  Retrieved from https://digitalfire.com/4sight/material/copper_oxide_black_237.html

I found a good resource: https://www.thespruce.com/oxidation-and-reduction-atmospheres-2745940