A supplier's glaze section runs to hundreds of products and most of them are variations on a handful of jobs: a transparent, a white, a few colours, and the specials that do something unusual in the firing. A first set of three or four covers almost everything, and a shelf full of half-used jars covers nothing.
The four glazes that do most of the work
A transparent, for anything decorated underneath. A white or off-white opaque, which is the base of most tableware. One dark, usually an iron brown or black, which flatters almost any body. And one colour you actually like. With those four and a body you know, you can make a coherent range, and everything else on the shelf is an addition rather than a foundation.
Ready-made and raw are different hobbies
Buying ready-made glaze is buying a result: consistent, tested, repeatable, and priced accordingly. Mixing from raw materials is buying control: cheaper per bucket, endlessly adjustable and requiring test tiles, scales and a respirator. Most people start with the first, and anyone making a lot of work eventually mixes their own transparent and white because those are used in volume.
Test tiles are the whole method
A glaze behaves differently on a different body, at a different thickness, in a different kiln. A tile of your own clay, dipped once and twice, fired in your own kiln to your own schedule, tells you more than any photograph. Keep them, label them on the back with an underglaze pencil, and a glaze library builds itself over a year.
Buying sensibly
Buy the volume you will use. A large bucket of transparent is economical and stores indefinitely; a large bucket of an unusual colour is a decade of storage. Small jars are for trying things. Suppliers list glazes by firing range and by finish, which is the order to filter in: range first, because the wrong range is unusable at any price.
Questions people ask about glazes
How many glazes do I need to start?
Three or four: a transparent, an opaque white, a dark, and one colour. Everything else is an addition to a working set rather than part of it.
Are ready-made glazes worth the money?
For colour variety and for small quantities, yes. For the transparent and white you use in volume, mixing from raw materials is much cheaper.
Why does the same glaze look different on my pots?
Thickness, body and firing schedule all change a glaze. That is why test tiles are made on your own clay in your own kiln.