The Glazing Process
We use one clear base glaze over a white body with the addition of Mason and Ferro glaze stains of 5% to 10%. When using these types of Raku glazes there are many things to consider for a positive outcome; -Bisque temperature of ware; If ware is bisque to high, glaze absorption can be uneven or it my be hard to get a thick enough coat for ample coverage and proper color density .
-Thickness of glaze application; If application is to thin the glaze will have a washed out look. If the glaze is to thick you can get pin holing, mottling or the glaze may run off the pot -Viscosity of glaze; In order to get a good glaze coat when dipping a reading of around 42-45 on a hydrometer should be about right, or you can weight test the glaze 500ml should weigh about 720 grams = 1.44 specific gravity. At proper specific gravity hold the pot under for about 20-25 seconds, this should give you a coat of about 2/100 of an inch, if the pot is bisqued to proper temperature (around 1000 degrees centigrade in oxidation depending on your clay body) when spraying (for larger pieces that are more difficult to dip) a reading around 40 is good. -Shape of ware to be glazed. Some shapes that have wide shoulders with a small foot can curtain if the glaze is too thick or over flocculated.
Two possible solutions are; when dipping when pot is emerging form glaze at end of dip remove very slowly form the widest spot down letting glaze sheet evenly to avoid curtaining. Spraying thou time consuming may be the only way to get an even coat. -Technique of glaze application, spray, dip; The technique of application should match the piece and the amount of glaze available, if you have a small amount of glaze, spraying or brushing may be your only option.
Dipping will take a container of glaze that is large enough to fit the piece with room to spare. I do not recommend pouring for even coverage with this type of glaze. -Evenness of application; All the information above relates to this topic, if care is not taken the color density will vary on piece and will not have an overall consistency.