In recent years hobby and even professional potters are been switching to buying bottled glazes and applying them by brush. They deem this worthwhile for the convenience and the greater variety of visuals achievable (as opposed to mixing ones own glazes). However application by pouring is particularly advantageous for certain shapes of ware (e.g. bowl and vase exteriors, flatware), to apply cover glazes (e.g. flat colors, transparents, whites) or for frequently used recipes one has in hand (e.g. rutile blues, stained base recipes).
Applying an engobe by pouring or spraying
An example of an engobe (slip) applied to dry ware and then fired at cone 2. The one of the left has been poured, the right sprayed. Control of the thickness of engobes is important, thus the specific gravity and viscosity of the slurries are very important. Engobes are invaluable since a red or brown burning body can be made to fire white like porcelain (enabling much better glaze surface quality).
Commercial glazes on decorative surfaces, your own on food surfaces
These cone 6 porcelain mugs are hybrid. Three coats of a commercial glaze painted on outside (Amaco PC-30) and my own liner glaze poured in and out on the inside (G2926B). When commercial glazes (made by one company) fit a stoneware or porcelain (made by another company), without crazing or shivering, it is purely an accident! So use them on the outside. But for inside food surfaces make or mix your own. When you know the recipe you can tune the thermal expansion. And the degree of melt. And the application properties. And you can use quality materials to source a balanced chemistry. The place to start understanding your glazes, organize testing and development and document everything is an account at Insight-live.com.
Pour Glazing a Large Terra Cotta VaseShow on Post Page
Much better than trying to paint to glaze on from little jars!