Alternate Names: Vinegar Solution 20%
Vinegar is often used in ceramic slurries to change the viscosity (thicken it). While there are more effective flocculants (e.g. calcium chloride, epsom salts), vinegar is popular among potters simply because it is so available.
The effect is to gel the slurry. When additions are done judiciously the degree of gel in a glaze suspension can be fine-tuned to produce a rheology that enables applying an even layer without runs (even on even dense ceramic bodies).
Of course, if there are carbonates in the glaze the acid can react with them (the thixotropy of the slurry will also be lost, theoretically because the reaction would produce CO2 and that would neutralize the acid). By-products of this reaction can have a negative effect on the suspensions ability to respond to epsom salts (if this happens calcium chloride should still work). Even if there are no carbonates, vinegar-flocculated slurries can thin out over time. When this happens just add a little more to reestablish the desired rheology.
When a slurry is very fluid (having a low specific gravity) vinegar may not be effective. In these cases epsom salts will often work (producing a more stable slurry as well).
Vinegar is also used in clay bodies to increase acidity to improve plasticity. The acid works to neutralize sodium ions (from water, leaching feldspars) that tend to deflocculate the clay. Excessive acid may tend to dissolve more feldspar or nepheline syenite negating the effect.
Slurries with more clay (like engobes, slips) generally respond better to epsom salts. However the extra clay also makes them more likely to go moldy, so you may need to add a few drops of Dettol to kill the bacteria (if they are stored for any length of time). Vinegar works better for glaze surries, but only if they have sufficient specific gravity. Many people like to make an epsom salts solution and add that, but if you have a good mixer you may find it more intuitive to add the crystals (which you should crush to a powder) and wait 30 seconds for the viscosity to respond.
Out Bound Links
Rheology refers to the array of characteristics that a ceramic slurry exhibits: its density, flow, thixotropy, permeability, viscosity, stability, etc. Technicians seek to understand and control the dynamics of the slurries they use (to maintain consistency and optimize them for the product and proc...
Magnesium Sulfate, HEPTAHYDRATE, hydrous magnesium sulphate
In Bound Links
Knowing about thixotropy will enable you to mix a glaze that stays in suspension much better. It does not drip alot when a piece is draining. It goes on evenly, of adequate thickness and does not run. It dries quickly (on porous bisque) and is just much nicer to use. The secret to all of this is not...