|10 inch (254mm) pitcher, earthenware, alkaline copper blue glaze over a white slip that is coloured pale green with chromium oxide.|
Really this firing was a test, as I wanted to see how the glazes worked over the slip coating that was on the pots. I have known some glazes to actually dissolve a layer of slip, so I wanted to be sure this sort of bad behaviour would not happen. I suppose you could say that the clay of the pot is like bare skin, in fact it is often referred to as "the body", and the slip coat is a sort of underwear, and the glaze is the outer layer of clothing! The layers of glaze and slip conceal and reveal the warm red coloured body beneath it, and there can be complicated and beautiful effects as colours are veiled and modified.
|Another view of the 10 inch (254mm) pitcher.|
I wonder if you also have "friends" that you like to visit in a museum collection?
|9 inch (228mm) pitcher, earthenware, alkaline copper blue glaze over white slip. Note that this is the same glaze as in the pitcher in the previous photo, but over a white slip this glaze gives a turquoise blue.|
|Close up of the alkaline copper blue glaze (over white slip coloured pale green with chromium oxide).|
This is my Copper Blue Glaze D for Cone 2 - 4 (with technical details supplied by Insight Glaze Software).
60.00 Ferro Frit 4110
20.00 Soda Feldspar
7.00 Ball Clay
5.00 Lithium Carbonate
3.00 Copper Carbonate
Thermal Expansion: 8.89
As an experiment I did try firing two of my alkaline copper blues to cone 10**, just to see what would happen. At cone 10 there was considerable bubbling of the glaze and some running and a shift in colour from blue to green.
|Alkaline copper glaze B and D. Back row fired at cone 3 and front row fired at cone 10.|
The remaining two pitchers have on the outside a commercial clear glaze that is available in this country called Abbot's Clear. I have modified this glaze with metal oxides. The first has 2 percent cobalt carbonate added. The glaze was poured over, and animated to some extent by the dribbles of thicker glaze.
|11 inch (280mm) pitcher, earthenware.Commercial clear glaze with added cobalt, over white slip with chromium oxide.|
|9.5 inch (241mm) pitcher, earthenware. Commercial clear glaze with yellow stain over white slip with chromium oxide.|
To be honest, it is a very useful glaze on the inside of things, and can look nice over white slip, but I do find it a bit sad to see it on the outside of an earthenware pot, as I keep thinking how much better a traditional lead glaze would look, very much in the way that lead crystal wine glasses look so much better than the "ordinary" wine glasses do. The trouble is that we are all afraid of lead these days in our grown-up modern society, so.. we have to just accept a boring alternative whilst thinking up other ways to kill ourselves and destroy the planet!
|Glaze tests. The one in the middle is the commercial clear glaze with 5 percent manganese dioxide added. The ones each side are both alkaline blue glazes over white slip.|
Some Cones that were mentioned in the text.*Cone 3 is about 1152 C (2106 F) when heated at 60 C/hr (108 F/hr)
**Cone 10 is about 1285 C (2345 F) when heated at 60 C/hr (108 F/hr)
***Cone 6 is about 1201 C (2194 F) when heated at 60 C/hr (108 F/hr)
Insight Glaze Software
Do visit The Digitalfire Corporation website for information about this glaze software.
The Age of Steam!
However.... the brave locomotive still had steam enough on its return journey to wail and moan a splendid ear jangling greeting as it passed us!
For more about the steam train and its fiery day out... here is a link to TV3's news article Oamaru steam train fires under investigation.