- “Above all, they are metal oxides. Metal oxides are compounds of oxide anions and metal cations. Most metals occur as oxides in nature, in their immediate natural state on earth, where oxygen is abundant in air and water. A pure metal exposed to air or water tends to combine with oxygen, depending on the ambient environmental conditions (temperature, pressure, pH, etc.), and the resulting metal oxide is the result of corrosion. Corrosion refers to the alteration of a material by chemical reaction with an oxidizing agent. www.smart2000.fr
“Experience shows that some metal oxides are ceramic colorants, i.e. their powder mixed with a paste or glaze adds color to the fired product. Here are a few examples of the most common oxides and the colors they impart to an oxidation-fired glaze: cobalt ( blue ), copper ( green, blue ), manganese ( brown, violet ), iron ( yellowish, reddish, greenish ), chromium ( green, yellow, red ), nickel ( brown, greenish, gray ), and others ( uranium, titanium, vanadium, etc. ). Color intensity increases with the level of oxide colorant. Color intensity depends on the covering power of the oxide (e.g. cobalt oxide, 0.1% of which will give a very strong blue, while the same amount of iron oxide will give a very pale hue). The color obtained by an oxide also depends on the characteristics of the product in ( or on ) which it is introduced. Take iron oxide, for example, which will give a yellowish hue in a paste rich in alumina, and a reddish hue when there is little alumina. Or copper oxide, which gives blue tones in alkaline glazes and green tones in lead glazes. Antimony oxide produces yellows (Naples yellow) in lead glazes, and is virtually colorless in other glazes. Intermediate shades can be obtained by mixing pure oxides. When too much oxide is added to the glaze, new hues, such as metallic hues, can be obtained by saturation. The firing temperature and atmosphere (reduction or oxidation) influence the color imparted by an oxide. The color of the oxide mixed with the raw glaze (or paste) is often very different from the color after firing. These complex and unpredictable behaviors explain the need for meticulous testing, but also the multitude of possibilities.” www.aude-lauvergnas-ceramique.fr
I set out to find rust. Well, it’s not easy at all, because today’s ferrous metals are all more or less anti-corrosion treated! But I did find some nice rust scale specimens, great harvest!!! Good jumble in the earth, mosses etc.
Strain once. 
Then sieve 80. 
Then hop long and hard to grind them into powder in the marble mortar. Yes it’s handmade ;))
And again with a 100 mesh sieve to obtain a satisfactory result.
It’s fascinating.
