Wax resist prevents glaze from adhering to pots for purposes of firing and decorating. It works by preventing water in the glaze from being absorbed into the bisqueware. The wet glaze remains on the surface, allowing it to be easily removed before firing. Wax can also be used on delicate attachments, thin rims, handles, joints, or repaired places to force these areas to dry more slowly.
There are many forms of resists, ranging from the traditional hot-wax paraffin or soy wax (heated to melt), to cold-wax resist emulsions (a mixture of two or more liquids that are normally unmixable like oil and wax or wax and water), including paraffin, water-based formulas, and petroleum-based formulas. There are also peel-off, latex-based resists and a number of DIY solutions using crayons, glues, oils, etc. Cold-wax resist emulsions can be brushed, sponged, or dipped.
Water-Based Cold Emulsions
Water-based emulsions are best for waxing bottoms, lids, attachments, and for decoration where you want raw clay to show through. I prefer Forbes wax from Highwater Clays (www.highwaterclays.com), because it’s a hard, durable wax resist that’s the most similar I’ve found to hot wax. Water-based emulsions usually contain paraffin and water and are highly susceptible to freezing.
2 Add a little alumina to the wax to prevent pieces from sticking together.
3 Use food coloring to make wax resist easier to see on light-colored surfaces.
4 Use cheap foam brushes for waxing large areas or lots of feet and rims.
Oil-based wax is great for layering between studio dipping glazes. It’s a stickier and thicker formula that won’t peel off removing glaze with it. Some prefer this type of wax for lids, bottoms, etc., but I find the stickiness to be an issue when wiping glaze away.
As a student nearly 17 years ago, I remember using hot paraffin wax. Hot wax beads up glazes beautifully, but it carries with it a heavy penalty to yourself and potentially your studio. Many potters melt old candles or gulf wax (commonly used in canning) in an electric skillet to use as a resist.
These types of wax begin to melt as low as 99°F (37°C) on up to 165°F (74°C) depending on their composition. Because melt points are widely varied, so are the flame points. Flame point is the temperature at which the wax can catch fire. Essential oils and additives like mineral oil or turpentine added to these types of wax can be especially dangerous. Flame points are known to be as low as 285°–425°F (141°–218°C). An electric skillet can easily get this hot and cause a studio fire. Spills and splashing can cause burns, eye and skin damage, etc. Danger signs to watch out for when melting wax are wax smoking, changing color, or sizzling.
In cold form, paraffin isn’t found to have specific toxicity or carcinogens. Unfortunately, MSDS sheets don’t have to show information about heated paraffin. Most people find the fumes from hot wax to be nausea inducing and uncomfortable to breathe—irritating to the lungs or an irritant that causes headaches. OSHA (www.osha.gov) recommends wearing a professionally fitted respirator with organic vapor cartridges when working near wax fumes. OSHA also cites specific air tolerances that most studios using melted wax are unable to test for. Anecdotal evidence from potters and universities using vent hoods indicates that even a hood doesn’t prevent students from feeling ill or having trouble breathing around melted wax. Many studios put wax dipping areas outside for this reason, but that doesn’t prevent potters from standing over the wax breathing in fumes while working.
5 For best results, let the wax harden for a few hours before applying glaze.
6 Always use a clean sponge when wiping excess glaze off wax resist.
Wax emulsions are also not risk free. When they burn in the kiln, they’re still producing fumes. Your kiln must be vented if you use wax. Because emulsions contain the same types of wax, any toxins, irritants, or carcinogens found in wax would be present as well.
I don’t feel that the benefits outweigh the risks to use hot wax in my own studio. We have made a complete switch to water-based cold-wax emulsions and have had great success using them.
In looking at online forum discussions, I’m still seeing many potters recommending hot wax and worse, hot wax with flammable additives.
Why risk burning down your studio? Though it can be hard to change established habits, safety in the studio is serious business. The risks of hot wax are just not worth it when cold wax is a perfectly good alternative and readily available from most ceramic suppliers.
Tips for Cold-Wax Success
Dip nicer brushes, used for decorating with wax resist, in dish soap first (1), or use a brush cleaning soap available from Mayco Colors. If your brushes aren’t coming clean, try spraying on Shout laundry stain remover as you clean. It helps to break up the wax, especially oil-based waxes.
If you’re using porcelain and using wax emulsions to coat the lid seat and lid edge, you can add a small amount of alumina to the wax to help prevent the porcelain pieces from sticking together, especially when firing at temperatures above cone 6 (2).
Add food coloring to the wax to make it easier to see where you’re applying it over light-colored clay bodies or glazes (3).
Use cheap brushes because wax resist is hard on them. I prefer to use foam brushes for waxing (4).
Wait a few hours in between waxing and glazing for best resist results. The extra time allows the wax to harden and the glaze beads up better (5). Minimize wiping waxed surfaces by doing it the same day you glaze using a soft sponge, preferably one that you don’t use with clay (6). A sponge that has grog trapped in it from throwing or cleaning surfaces quickly wears down wax, which is a common complaint about wax resist.
Thin wax emulsions for easier brush ability or dipping. If you’re using an oil-based wax, allow for a longer drying time, up to 30 minutes.
Deanna Ranlett is a frequent contributor to Pottery Making Illustrated. She owns MudFire in Decatur, Georgia, (www.mudfire.com).