Natured Inspired Firing Sinead Glynn

Appears in the Mar/Apr 2017 issue of Pottery Making Illustrated.

I’m inspired daily by the world around me; my interests range from the microscopic to the celestial. I’m also fascinated with how material, process, and form relate to one another. I explore the co-existence of the unique with the similar by creating multiples with various surface finishes and using natural materials that dictate the final outcome.

When creating my forms, I prefer slip casting. I enjoy the precision and problem solving of mold making and the repetition of slip casting. Slip casting allows me to create similar multiples where the variation in each piece comes from the seemingly uncontrollable effects of the raku firing process.

Ferric-chloride firing is a unique alternative firing process I use, alongside other bare clay techniques. The effects of ferric-chloride firings are impossible to reproduce, which adds to the individuality of each piece.

Choosing a Clay Body It’s important to choose a clay body that will withstand thermal shock as the fluctuating temperatures involved with raku firings can cause the ceramic to fracture. A mid- to high-fire clay body that contains grog is ideal.

Ferric Chloride Application

I prefer to use a combination of dipping and pouring to apply the ferric chloride onto the pieces. Layering different amounts of ferric chloride can also cause different reactions in the firing process. It’s important that each layer is allowed to soak into the ceramic form, then dry before the next layer is applied (3).

Many different combustibles can be used in the firing process, each giving a different color or pattern effect. Applying sugar to wet ferric chloride causes a halo effect after the firing. Dip the form into the ferric chloride to get another thin layer prior to sprinkling a small amount of sugar on the surface (4). The ferric chloride dries around the sugar crystal, so care must be taken not to disturb the surface during the next stage (5). Set the form aside to dry completely. It’s really important that the ferric chloride has dried completely before coming in contact with tin foil.

Ferric Chloride Safety

Ferric-chloride firings, like other alternative firing techniques, require careful planning and specialized safety equipment. This particular process produces vapors during the firing that are an inhalation hazard. Ferric chloride is an etching fluid and should be handled with great care. It’s corrosive and harmful if inhaled or swallowed. Every precaution should be taken to reduce any risk while using this technique. Prior to using ferric chloride, please read its material safety data sheet for potential health risks and effects (available at www.sciencelab.com). Always use and store ferric chloride (a liquid) in a sealable plastic container. Place the bottle in a separate plastic box lined with newspaper to catch any overspill that may run from the bottle while you’re using it.

Wear two pairs of latex/non-latex gloves and safety glasses to protect your skin and eyes from spills or splashes. A vapor respirator should be worn to protect from fumes. Only use this liquid in a well-ventilated room, or outside,  and have running water close by in case of an emergency. Wear an apron to protect your clothes (1, 2).

Choosing Combustibles

A combination of the fumes from the combustibles reacting with the ferric chloride and the foil saggars creates various fuming patterns and colors. Varying the combinations of combustibles will give you even further color opportunities. After many experiments, I have found my favorite combinations, but this is where you can experiment. I use poppy and sesame seeds, used coffee grounds, herbal teas, onion skins, and various dried seaweeds. Horsehair, copper carbonate, and various oxides can also be used (6).

Foil Saggars

Various grades of foil can be used, but a thicker variety is better. Altering the number of foil layers will also affect the end result. As the bottom of the kiln is hotter than the top, use more layers to wrap the saggars that will be placed on the bottom shelf.

Prepare the saggars by spraying cheap hairspray on a layer of foil. Allow this to dry for a few minutes until it becomes tacky/sticky (7). At this point, sprinkle on a small amount of seeds, copper carbonate, and any other light combustibles. The hairspray holds these combustibles in place when you wrap the form, stopping them from sinking to the bottom of the saggar. Place the dry, ferric-chloride covered form into the center of the foil sheet. Add heavier combustibles like seaweed, onion skins, and/or horsehair on or around the form (8). Take care not to overload the combustibles, as too much will cause a blackening of the form. Carefully wrap the first layer, allowing some space between the form and the foil where the fuming will take place. If the foil is wrapped tightly against the form, a different effect can be achieved. Continue to wrap the saggar with three or four layers of foil (9).

Raku Firing

The raku kiln should be set up outside, keeping in mind what direction the wind is blowing. The fumes that are created during the firing process are highly toxic, so work upwind. Remember that when you go to open the foil saggars, they need to be placed so that you are still upwind of any lingering fumes to reduce your risk of inhalation. It’s also important that these fumes don’t come into contact with unsuspecting neighbors and/or animals, so choose an area to fire the kiln that possesses the least amount of risk. A vapor respirator is essential throughout the entire firing and cooling process. I also use a full-face shield to protect my eyes from both heat and fumes. Welder’s gloves and an apron will provide added protection from the heat (10).

The saggars can be placed individually on each shelf (11), or tumble stacked. Begin the firing slowly. After approximately 20 minutes, hold the temperature between 446–500°F (230–260°C) for anywhere between 6–8 minutes. This allows the combustibles to begin fuming. The gas will need to be tweaked continuously for this temperature to be held for the required time. Moderately raise the temperature above 1112°F (600°C) over the next 20 minutes; the last part of the firing can be done over the next 10 minutes depending on what result you’re aiming for. Generally speaking, the firing results I desire take approximately 1 hour. The top temperature also varies from between 1382–1652°F (750–900°C). Purples, pinks, and whites are achieved at the hotter temperatures while yellows, oranges, and reds are gained at the lower temperatures. However, this technique requires much experimentation, as so many variables will affect your end result. Keep a record of all your results so that a similar effect can be achieved in the future.

Cooling, Cleaning, Sealing

Once the top temperature is reached, turn off the kiln and allow it to cool a little before opening. Carefully remove the saggar and place it on the ground, open the saggar slightly to allow the fumes to disperse. If you’ve fired to the higher temperature, the foil will have started to disintegrate, so extra care is needed when removing it from the kiln.

After the fumes have dispersed, open the saggar completely. When the pieces are exposed to the air they begin to cool and the colors will develop. Very often they’re quite dull to begin with but the colors become more vivid when the temperature drops. Once the forms are cool enough to handle, remove any ash deposits with a soft brush (12).

Finally, seal the forms with an acrylic spray; semi-gloss, gloss, or matte finishes can be experimented with. The sealer intensifies the color and protects the surface from dirt and dust. Use light layers to avoid any unsightly drips and allow the surface to dry completely between layers.

Sinéad Glynn received her B.Des (Hons) degree from the National College of Art and Design (NCAD), Dublin, Ireland. She teaches various ceramic programs in adult education around Ireland and continues with her own practice experimenting with various techniques. To see more of her work visit www.sg-ceramics.webs.com.

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