Alternate Names: Stannic Oxide, Tin(IV) Oxide, Tin Dioxide, SnO2
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Tin oxide is a white or off-white powder produced by oxidizing molten high grade tin metal. It is typically quite pure, some manufacturers have grades up to 99.999% purity.
Tin oxide has long been used to opacify glazes in oxidation (make transparents opaque) at all temperatures. Hand decorated tin glazed earthenware of the 1700/1800s is the most famous use of tin in glazes (delftware-England, faience-France, maiolica-Italy). While many potters are keeping this tradition alive today most now use zircon based opacifiers instead. Thus any discussion about the use of tin oxide as an opacifier ends up comparing it with zircon products:
-Twice as much zircon is required to produce the same level of opacity.
-Like zircon, tin melts at very high temperatures and thus does not go into solution in typical glaze melts.
-Zircon will stiffen the glaze melt more than tin.
-Zircon will likely produce a harder glaze surface.
-Zircon will reduce the thermal expansion of the glaze more than tin.
-The quality of the white color is different (tin tends to be more of a blue white, zircon a yellowish white).
-Tin is very expensive, this is likely the main reason for its much more limited use as an opacifier today.
-Zircon tends to have less of an effect on the development of metal oxide colors (e.g. tin reacts with chrome to make pink).
-If gloss is an issue, silica might have to be reduced to compensate for the silica introduced by a zirconium silicate opacifier being substituted for tin.
-While there are other products that produce varying degrees of opacity, none are as neutral and non-reactive as tin and zircon. Other opacifiers also tend to variegate the glaze.
-Tin does not normally opacify in reduction firings.
Tin is also a player in the development of ceramic colors, for example chrome tin pinks and maroons. Tin with iron in oxidation makes a warmer shade of brown than zirconium does.
Tin oxide is also a variegator. For example, tin can react with titanium and rutile to to completely transform the color and character of a glaze. Although tin is expensive, very little is required to produce stunning effects in many colored glazes.
Some claim that a little tin (not enough to opacify) will add extra smoothness and shine to many glazes.
Glaze Opacifier - White
As little as 4-7% can produce brilliant white, although it is more typical to use 8-10% for full opacity. However, be aware that even tiny amounts of chrome in the kiln will volatilize and combine with the tin to produce pink shades.
Glaze Variegation - Tin/Iron Effects
Tin reacts with iron in fluid glazes to produce variegated surfaces. A good example is the Albany Slip 85, Tin 4, Lithium 11 glaze for cone 6.
This is a 45:27:28 Gerstley Borate:Kaolin:Silica base on a dark firing clay body. But tin oxide will do that in almost any cone 6 clear glaze (use one that fits your clay body).
These two are the same Alberta Slip glaze, except the one on the right has 4% tin added (to the base which is Alberta Slip 80, Frit 3134 20, Rutile 4).
On Plainsman H443 iron stoneware in reduction firing. Notice Tin does not work. Also notice that between 7.5 and 10% Zircopax provides as much opacity as does 15% (Zircon is very expensive).
Same body, same glaze. Left is cone 10 oxidation, right is cone 10 reduction. What a difference! This is a Ravenscrag Slip based glaze on a high-fire iron stoneware. In reduction, the iron oxide in the body and glaze darkens (especially the body) and melts much more. The behavior of the tin oxide opacifier is also much different (having very little opacifying effect in reduction).
Right: Ravenscrag GR6-A transparent base glaze. Left: It has been opacified (turned opaque) by adding 10% Zircopax. This opacification mechanism can be transplanted into almost any transparent glaze. It can also be employed in colored transparents, it will convert their coloration to a pastel shade, lightening it. Zircon works well in oxidation and reduction. Tin oxide is another opacifier, it is much more expensive and only works in oxidation firing.
This is a melt fluidity test comparing two different tin oxides in a cone 6 transparent glaze (Perkins Clear 2). The length, character and color of the flow provide an excellent indication of how similar they are.
Out Bound Links
Tin oxide mineral.
In Bound Links
A glaze additive that transforms an otherwise transparent glaze into an opaque one. Common opacifiers are tin oxide and zircon compounds. Opacifiers typically work by simply not dissolving into the melt, the white suspended particles thus reflect and scatter the light. Since they do not participate ...