Zirconium opacifiers are what most modern white glazes are built on. They do the same job as tin oxide, turning a transparent glaze opaque white, at a small fraction of the cost, and they give a harder, colder, brighter white that suits contemporary tableware.
How it compares with tin
Zirconium is used at higher percentages than tin, typically eight to twelve percent against five to eight, and still costs far less per bucket. The white it gives is brighter and cooler where tin's is creamier and softer. Neither is better; they are different whites, and a line blend of both on your own base settles the choice faster than any description.
Behaviour with colourants
Zirconium is chemically inert in the melt and does not produce the surprising interactions tin does, which is usually an advantage. Colourants added over or into a zirconium white behave predictably. It also stiffens a glaze slightly at the percentages used, which can reduce running in a fluid base, occasionally to useful effect.
Where the white goes flat
At high percentages a zirconium white can read chalky and dead, particularly on a flat form with no variation in thickness. The usual remedies are to reduce the percentage slightly, to accept a semi-opaque glaze that shows some of the body, or to add a trace of a colourant so the surface has somewhere to break.
Buying and handling
Sold as zirconium silicate under several brand names, all doing the same job with slightly different particle sizes. It is inexpensive by the kilogram and used in quantity, so it is one of the materials worth buying in a larger bag. It is a fine powder with the usual weighing precautions.
Questions people ask about zirconium dioxide
Is zirconium as good as tin?
It gives a different white: brighter and colder against tin's creamier one, for a fraction of the price. Most commercial white glazes use zirconium.
How much do I need?
Usually eight to twelve percent against five to eight for tin. Test a line blend on your own base.
Why does my white glaze look chalky?
Often too much opacifier on a flat form. Reducing the percentage or adding a trace of colourant gives the surface somewhere to break.