Stefanie Smith Ceramics


The Smoke Firing Process

Smoke firing is a process where ceramic pieces are coloured and marked by smoke rather than glaze.  It is an ancient method of firing and remains a primary firing technique in many cultures around the world.  Having largely been replaced by more complex and controllable high-firing kilns and glazing techniques in the West, smoke firing continues to be explored by those of us who are excited and inspired by its ability to create unique surface and colour effects.  It is a very immediate and hands-on firing process that requires a special combination of experience and willingness to relinquish ones control to the fire.  Every smoke fired piece features a unique pattern of colour and smoke--a element of the process which excites me to no end.  I love the surprise that comes as each piece is removed from the ashes and reveals itself once cleaned and polished.

HOW IT WORKS

Smoke firing typically involves layering clay pieces with fine combustibles such as sawdust, manure, newspaper, or dried plant materials. Typically the pieces and fine combustibles are topped with larger logs or grasses which, when lit, work to sustain the fire while generating enough heat to cause the sawdust/manure to smolder and generate smoke, and also to trap the resulting smoke around the pieces.

As it burns and smolders, the inner environment of the fire becomes oxygen starved, causing the carbon molecules of the smoke to embed into the clay as they seek to remove the oxygen residing in the clay material.  This process causes the darkening of the work.  The more tightly the smoke is contained in the firing, the blacker the pieces will be coloured. 

Smoke firing is not purely limited to blacks and greys.  By selectively adding specific oxides and organic materials you can generate a broad range of colours, from deep earthy reds and toasty browns, to rich blues and acid greens.  Banana peels, seaweed, coffee grounds, and orange peels are just a few of the everyday materials that can enrich a ceramic piece with surprising colour.

(Right: Sample of colour achievable with smoke firing)

Pit fired tealight holder by Stefanie Smith

SMOKE FIRING METHODS

There are several different methods of smoke firing, the most common being pit firing, saggar firing, and barrel firing. Each method is distinguished by how the fire and smoke are contained. 

Pit firing involves placing the pieces and combustibles in a pit dug or constructed into the ground.  It is likely the earliest form of firing and is excellent in its ability to be executed in a wide range of sizes; a  pit can be dug to hold one piece or a hundred pieces, depending on the artist or community's needs.  How the pieces are stacked impacts how each piece is smoked, and experienced practitioners can achieve specific results through diliberate layering.

Pit Fire

Saggar Firing involves placing each piece in its own container along with the fine combustibles and colourants. This container, or 'saggar' is typically placed in a kiln and fired to a temperature that allows the combustibles to burn out while containing the resulting smoke around the piece.  This method can allow greater control over end results as each piece is in its own preplanned blend of materials. The saggar itself can be made from a variety of materials, such as bisqued clay, paper, foil, or metal.

(Right: Aluminum foil saggar pieces being removed from a raku kiln)

Saggar Fire


Barrel Firing
consists of layering the combustibles and clay works in a barrel-- usually a trash can or old oil drum.  It offers similar results to pit firing while having the convenience of portability and better containment.  This is the method I use as I find it well suited to working in an urban environment where space limitations and proximity of neighbours are important considerations.

Barrel Firing

BURNISHING

Burnishing is a surface finishing technique often used in unison with smoke-firing.  Originally done to increase the strength and water-holding properties of early functional pieces, the technique is now frequently used for aesthetic purposes.  It is a process that creates beautiful smooth and glossy surfaces reminiscent of polished stone, and I find it also shows off the nuances of the smoking effects more strongly than an untreated surface.

Burnishing is achieved by carefully rubbing the unfired clay surface with a smooth object (a beach stone is my tool of choice). This action compresses and aligns the clay particles to create a denser, smoother, and more reflective surface.  I regularly do two rounds of burnishing, the first using water as a lubricant, and the second using vegetable oil.  Once the piece is dry it is bisque fired in a kiln, smoke-fired, and then coated with a thin layer of wax, shellac, or acrylic varnish to enhance the burnished surface.