Glaze Application Techniques

BRUSHING
Our Brushing Medium (Product Code CB180) and Painting Medium (Product Code CB160) have been developed so that they may be mixed with powdered glazes, stains etc. by simply stirring with a cake beater or paint stirrer and running the liquid through an 80 mesh sieve.

Suggested proportions are:

  • For lead-free glazes, approximately 1 litre of medium to 1 kg of powder.
  • For lead-bearing glazes, approximately 500-600 ml of medium to 1 kg of powder.
  • Mediums will not deteriorate with time and are non-toxic.

CHOOSING THE RIGHT BRUSH
A suitable brush must be used or the results can be very different from those desired.  We recommend square or oval brushes such as hake or square shaders as these will accept a good load of colour.  We recommend a brush 20-25 mm in size for average sized pieces.

LIQUID GLAZE ( BRUSHING GLAZE)
Liquid glaze is prepared ready to use.  However, as materials in some glazes tend to settle after standing, it is important to shake or agitate the container vigorously, then stir, before use.  If after shaking and stirring the glaze it is still too thick to load a glaze brush easily then it may be necessary to add a little water.

PRIOR TO GLAZING
Bisque fire the ware to its recommended temperature (minimum 1000°C).  Sponge bisque with a damp sponge to remove any dust which may have collected.  On narrow necked pieces where a sponge cannot work, use a clean damp brush.  Do not eat, drink or smoke whilst handing your work as any grease transferred to the bisque will resist glaze.  Although it may appear to cover grease spots when applied, glaze may crawl away when fired.

APPLICATION OF BRUSHING GLAZE
Once the container of liquid glaze has been shaken and stirred, load your glaze brush by immersing the hair up to the ferrule.  Remove the glaze from one side of the brush and apply the fully loaded side to the bisque.  Apply one even coat, let the “wet” look disappear, then apply a second coat in the opposite direction. When the second coat has lost its “wet” look, apply a third coat in the same direction as the first.

GLAZING THE INSIDE OF NARROW NECKED PIECES
This process should be done before application of the exterior colour.  If using brush-on glazes exclusively, it will be necessary to thin some down for rolling the inside of any ware that cannot be reached by a brush.  Do not thin down a whole jar unless it is to be used only for rolling.  The addition of water will vary according to the original consistency, however as a rough guide, use three parts liquid to one part water.  Replace lid and shake thoroughly.  Pour thinned glaze into ware and roll piece around so the glaze can cover all internal surfaces. Pour out slowly whilst still rolling so the glaze can cover the internal lip of the ware.  Leave upside down for five minutes to drain.

CADMIUM SELENIUM GLAZES
The toxic glazes containing Cadmium & Selenium are bright and vivid, lending themselves to decorative pottery.  However, to achieve these brilliant results care must be taken with their application and firing as they are more sensitive than other glazes.  Lead free and zircon encapsulated stains are used in glazes like Brick Red and Hot Orange.  This makes them perfectly food and drink safe.
The following suggestions are given to assist customers to get the best results.

CADMIUM SELENIUM GLAZE APPLICATION

  • These glazes should only be applied to hard-fired bisqueware.
  • Glazes should be applied about the same thickness as the average coloured opaque glazes. Pieces glazed too thinly tend to show clear breaks or patches. If glazed too thickly pieces may develop an ‘orange peel’ or rippled surface, or black spotting.  Make sure all pieces are thoroughly dry before setting into the kiln.
  • If too much water has been added inadvertently to the glaze, do not let the glaze settle and pour off excess as is normally done with other glazes.  In such a case, add more dry glaze until the desired consistency is achieved.

CADMIUM SELENIUM GLAZE FIRING

  • These glazes are intolerant of steam and other kiln gases.  For this reason, only dry ware (previously bisqued) should be set;  do not attempt to fire greenware along with these glazes.  Greenware should be fired separately to avoid other glazes “striking” them, causing loss of quality, patchiness, blackening or blistering.  Electric kilns are preferred;  if a gas kiln is used, the pieces should be set in saggars or the kiln must be fully muffled.
  • Do not overcrowd the kiln, or place pieces too close to elements, walls, kiln furniture, etc., or blistering or clear and/or blackish patches may result.
  • Firing temperatures vary with the time taken over approx. 700°C.  For a rapid fire, say 6-7 hours to peak, the glazes will withstand 1000 -1040°C.  For slower fires, the temperatures should be reduced somewhat.  Excessive rapid cooling (by opening the doors etc.) is not necessary but plugs should be removed as soon as firing is completed to ensure a naturally rapid cool.
    Some experimentation may be required to find the optimum procedure for the potter’s own conditions

POWDERED GLAZE

SETTING UP A GLAZE FOR DIPPING
Wearing a suitable mask, sprinkle the glaze powder into a suitable container of water and stir thoroughly.  Leave to settle overnight and pour off surplus water.  Stir, sieve through an 80 mesh or finer sieve, then add water if necessary to achieve the desired consistency.  This depends upon the porosity of the bisque ware but will be around 875-1225 gm of lead free powder to 1L of water.

When some liquid glazes settle out, particularly over a long period of time, they sometimes set hard at the bottom of the container, making them difficult to re-mix.  Others may settle during use and consequently demand thorough stirring or agitation during the dipping session.  To correct this defect, a flocculant or ‘anti-set’ solution should be added a little at a time, stirring it in very well until the settling stops.  Add carefully or the glaze will dry slowly on the ware and may cause ‘mud cracking’ and perhaps ‘crawling’ during firing.  The opposite effect of settling is when the glaze appears like thin custard and has a ‘creamy’ feel.  The glaze dries slowly on the ware or peels off during drying.  Some glazes that have a high clay content, or raw zinc oxide, magnesium carbonate, talc, etc., or have had excess dosing of ‘anti-set’ will have this defect.  The cure is to add very cautiously, small quantities of a 10% solution of Soda Ash or Sodium Silicate, stirring well, until normal drying and behavior occurs.

APPLICATION OF PREPARED GLAZE
Use either a bucket or glaze wok.  The type of glaze and the effect desired will indicate how the ware should be dipped:  transparent glazes should be thinner than opaque ones so dip once only.  A rutile glaze may be dipped once or twice for varying colour effects.
Walker Ceramics dipping glazes are delivered with a litre weight of 1500-1750 grams/litre (Specific Gravity (SG) of 1.5-1.75) depending on glaze composition.  Adjusting the glaze to a slip suitable for individual preferences requires the following:
Essential:  Dispex, Epsom Salts, volume measuring container, scale with 1 gm tolerance.
Optional :  Ford Cup #4 (or Paint Viscometer), stop watch.

Procedure
Adjust the litre weight to between 1400-1500 gm/litre (Specific Gravity of 1.4 – 1.5) by adding clean tap water to the slip.
The glaze slip should have the viscosity of evaporated milk or slightly higher.
If glaze slip is too thick, add Dispex (Product Code CB80) drop by drop until viscosity is satisfactory.
Never add water once you have Specific Gravity correctly adjusted!!
If glaze slip is too thin, add Epsom Salts solution drop by drop until viscosity is correct.
(To make Epsom Salts solution, mix 300 gm of Epsom Salts with 1 litre of hot water.)
It is highly recommended to use a Ford Cup or Viscosity Cup and aim for run-out time of 15 to 20 seconds.
After application the glaze layer should be as thick as the diameter of a standard steel paper clip.