White glaze problems

[Kate Monckton Ceramics]

I don’t know why my white gloss glaze just won’t cover properly. From when I initially dip the piece in the glaze to when it’s been fired. It comes out looking drippy and messy. I just don’t know what I’m doing wrong! 

[Bill Kielb]

Definitely post pictures as an example and provide info on the glaze, cone it’s fired to, claybody you are using.

[Hulk]

Hi Kate!

Mixing your glazes well and keeping them well mixed whilst dipping - that's one variable. If there's any bits or chunks, sieve the glaze - that's another variable.

 

How "wet" the glaze is - ratio of water to solid matter - can be expressed in terms of specific gravity:

Specific gravity (digitalfire.com)

I'm running between 1.39 to 1.47 (per my notes - keep notes!!) for the several glazes I use, mostly mixed from raw materials (I don't plan to buy any more premix, but do plan to use the premix I do have until gone - a powder blue, bad clear, and a matte white). A wetter glaze allows a wider (longer) "window" of dip time to achieve desired thickness, but will take longer to dry. A wetter glaze may also be more prone to running/dripping, however, the undesirable movement can be ameliorated! A less wet glaze typically goes on too thickly.

 

How the glaze moves can be adjusted:

Thixotropy (digitalfire.com)

This is the hot tip! A wetter glaze that has been adequately "gelled" goes on like a dream! I'm not having to rush to avoid a too thick glaze layer; a shake or two takes care of drops at the rim; any remaining drops I'll just run around the rim; any other remaining drops, I'll wait several seconds for the glaze layer to loose its sheen, then smooth the drop with a wet finger*. Glazing (almost all dip/pour - very little brushing, no spraying) is much more fun for me now.

As I typically don't glaze fire twice a month (if that), I start out with thorough mixing, sieve, then check/adjust specific gravity, leaving thixotropy check for last. Turning the glaze with a large kitchen whisk (clockwise, easier on my hand, elbow, etc.) to the meter of "Positive Vibration" (Bob Marley's 1976 album), when stirring is ceased, I expect:

    the glaze to turn as a mass, with very little shear (iow, not much currents of differing speeds);

    the mass to continue turning for about three to four turns;

    the mass to slow and stop all together - again, very little currents of differing speed;

    the mass to "bounce back" a bit when it stops.

The desired behaviour - liquid when moving, gelled when not moving - is much more conducive to successful glazing than the "liquid until it dries" extreme (imo).

Inadequately gelled glaze will exhibit currents of differing speeds as it turns in the bucket (use round buckets; square buckets are bad, heh) - a portion of the glaze will just keep on spinning for quite some time, whilst shearing against the portion of glaze moving at a slower speed.

*Some prefer to allow droplets to fully dry, after which they can be levelled by "fettling."