Liquid glazes are formulated for brushing.

Dry glazes are formulated for dipping, pouring and spraying.  

As a rule of thumb, for 1 lb of dry glaze powder, use 11 ounces of water for dipping glaze, 8 ounces of water for spraying glaze, or 7 ounces of water for brushing glaze.  Or, 25 lbs makes about 3 gallons.  

To use a dry glaze for brushing, a brushing medium, such as CMC powder may be added.  CMC acts as a binder and allows the glaze to flow smoothly. Mix CMC with a small amount of warm water and age for a day or two.  Prepared liquid mediums are also an option.  Then blend as below.  

To mix a dry glaze, first add bentonite to the dry glaze to keep it in suspension and increase the drying time.  Bentonite is mixed at approximately 2 grams (.0044 pounds) per pound of dry glaze.  Measure water into a clean plastic bucket.  Mix the measured amount of glaze into the water as best as you can.  Then pour the mixture through a sieve into a second bucket, pushing the clumps through the sieve with a rib or other tool.  Repeat several times.  (Note: Glaze recipes sometimes specify a mesh to use, and that will affect the outcome of the glaze.  Otherwise, for glazes, 80-100 mesh are most common.  (Lower numbers are usually for mixing slips.)

Optimally, a hydrometer should be used to check the viscosity of the mixed glaze.  The hydrometer reading should be approximately 900-1000 for dipping, 1500-1700 for spraying, and 2200-2500 for brushing.  

Let the glaze sit for 24 hours, remix, then use.

Glaze should be stirred often, as contents can settle during use.  If the glaze thickens over time, just add water.  If you don't have a hydrometer and your glaze recipe doesn't call for a specific thickness, a general guideline used for dipping glazes is "the thickness of low fat milk."  

Some people find that if they use a power mixer they don't have to sieve their glaze.  The sieving process accomplishes 2 things.  1) Makes sure the glaze is well mixed, and 2) Gets rid of lumps.