Salt-glaze
Salt-glaze is the dynamic process I use to decorate and glaze my pots. Common salt along with sodium carbonate (washing soda), is added during kiln firing to the fireboxes. The chamber at this point is white hot, approximately 1200ºC. The heat of the firebox forces the salts to vaporise into their gaseous elements. It is the sodium element which combines with the clay itself and any slips applied to it, to create a range of beautiful and serendipitous glazes.
The origins of this salt-glaze process are somewhat uncertain and undocumented. The very first salt-glazed stonewares appear to have been made in the Rhineland, Germany during late 13th or early 14th centuries. It seems probable that a group of potters firing and then unpacking their kiln, noticed that a new source of timber yielded a thin glazed surface to the otherwise bare clay, and that this timber for whatever original purpose was impregnated with common salt. Here began several hundreds of years of inspiration and exploration for peasants, potters and artists alike.
If you are interested in further reading on salt-glazing, please view publications under CV.
This slideshow illustrates and describes the range of processes associated with salt-glazing
Soda-wood boards await application to fireboxes
Prior to the salt-kiln being packed, larger pots are often measured and their placement in the kiln considered before the pots leave the studio
Small balls of refractory wadding are glued to all pot bases before firing, to prevent the sodium sticking the work to kiln shelves
Prepared wadds: Composed from fireclay and sand, or alumina hydrate, wadding is the highly refractory material used to separate pots from kiln furniture. The salt would otherwise fuse the pots to the shelves. Kiln props and other furniture is wadded for the same reason
Wadding underside of a jug; this mix is made from fireclay, sand and sawdust which leaves a warm halo of colour on the fired pot
Salt and soda is prepared before the firing day. Salt is weighed into 100g newspaper packets. Sodium carbonate is brought into solution with boiling water and pasted onto thin wide pieces of wood
Plate batts
Raw pots are placed strategically, present with the knowledge of flame & sodium paths, along with the experience of previous results
Kiln pack: The back two bungs of raw pots are complete, the front two bungs of shelves are staggered 4″ from the back two, to encourage more diverse flame path and sodium build up
Sodium boards: anhydrous sodium carbonate is made soluble in boiling water and pasted onto thin wide boards. These are added to the fireboxes along with packets of salt, over 2 -3 hours, from 1200ºC
Kiln firebox (chamber temperature 1200ºC) Fuel combustion and salt volatilization, sodium boards applied to firebox
Jug close-up
Ash-glazed herringbone roulette
Glazed detail
Salt-glazed motif
Salt builds up firing upon firing, resulted in thick glaze on the kiln fabric. Some of this salt re-volatilizes during firing and beneficially assists with glaze formation
The salt and sodium have a destructive effect on the kiln fabric. Repairs are made periodically, here the base plate and bagwall have been partially removed
Unpacking a narrow shelf