Is Iron Oxide a colouring agent or Glazing material for Stoneware products?

Question

We make stoneware Salt Glazed pipes and fittings by coal firing method. Since we donot get good colour on bottom rows in our down draft kilns we tried to experiment with using GERU i.e. clay with high iron oxide content. This gave very good results but we are being told it will be considered as glazing and not colouring. We need the clarification whether applying clay with high iron oxide content will be taken as glazing or colouring and whether this clay will be called glaze or colouring agent?

Answer 1

Generally speaking if you mixed the GERU completely with your usual clay, it is coloring. A top coating would be considered as glazing by most (and for terracotta, the color must extend throughout and not just be on the surface).

Most stoneware is made entirely of Geru clay. This is part of the expense of making the items.

Answer 2

IRON OXIDE BLACK is ferrous oxide and produces various shades of brown or green when used as a glaze colorant or decorative oxide. In a high fire, matt glazes, iron oxide and titanium can produce reddish colors

im in ceramics class and we just talked about this on thursday.

Answer 3

Altogether there are 16 known iron oxides.[1]

These compounds are either oxides (Hematite, Magnetite, Maghemite, β-Fe2O3, ε-Fe2O3, Wüstite), or hydroxides and oxdide-hydroxides (Goethite, Lepidocrocite, Akageneite, Schwertmannite, Feroxyhyte, δ-FeOOH, high pressure FeOOH, Ferrihydrite, Bernalite, Fe(OH)2, green rusts).

Some of these oxides are used in ceramic applications, particularly in glazing. Iron oxides, along with oxides of other metals, provide the colours in some glazes after being fired at a high temperature. They are also used as pigments (see Category:Iron oxide pigments).

[edit] Iron oxides
Corrosion
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Corrosion

* Iron(II) oxide or ferrous oxide (FeO) The black-coloured powder in particular can cause explosions as it readily ignites.

* Iron(III) oxide or ferric oxide (Fe2O3) known in its natural state as rouge or hematite (also 'haematite'), but also purified for use as a coating in magnetic audio and computer media, where it is known as ferric oxide. In a dry or alkaline environment it can cause passivation and inhibits rust. It is also a component of rust.

* Iron(II,III) oxide or ferrous ferric oxide (Fe3O4), better known as the black-coloured mineral magnetite or lodestone also seen on Mars. Also a main source of iron, magnetite is an iron ore. This form of iron oxide tends to occur when iron corrodes underwater, and so is often found inside tanks or below the waterline of ships.

[edit] Iron hydroxides

* Iron(II) hydroxide Fe(OH)2. green colour.

* Iron(III) oxide-hydroxide FeO(OH) found as the mineral goethite. Red-brown colour. Also found as the minerals siderogel, limonite and feroxyhyte. There is a variant known as lepidocrocite.

* Iron(III) hydroxide Fe(OH)3. Dark brown.