Super Salt Glaze and Slip Recipes: An Excerpt From Our New Free Download The Salt Glaze Surface

Salt firing and salt glazing have been common practice in ceramics for centuries, initially as an industrial glazing method, and then as an artistic treatment and technique in studio ceramics. Not only does salt glazing seal the ware, but it creates a distinctive orange-peel texture that has become a desirable decorative trait of salt glazed ware.

Today, I am presenting a Will Ruggles and Douglass Rankin slip recipe and tips for salt firing. In addition, potter Cathi Jefferson explains how she used these recipes combined with terra sigilatta and Andrew Wong’s Luster Glaze to make the beautiful checkered surface shown here.  – Jennifer Harnetty, editor.


Will Ruggles and Douglass Rankin have been admired for their wood-fired, salt glazed work for years and their slip and glaze recipes have been trusted and used by many professionals for years. They use salt cups in their firings. The ware is stacked in the kiln with salt cups (made of wadding material) filled at the outset, and as the temperature increases, the salt vaporizes and adds just the right amount of sheen to these plates. You can see what salt does to the shelves in this kiln (salt will find silica to react with anywhere it can), and this is why it is necessary to have a kiln and shelves dedicated only to salt firing. If these shelves were used in a kiln that had not been salted, the salt on the shelves would re-vaporize during the firing and salt that kiln and the ware in it.

My Checkered Salt Fired Surface
by Cathi JeffersonI prepare terra sigillata by mixing 4500 grams Cedar Heights Redart or Kentucky Ball Clay (OM 4) into 3 gallons water and 48 grams lye (or Calgon). After this mixture settles for at least 24 hours, I siphon off the top two-thirds for use. For a dark outlining slip, I add 5 tablespoons of Mason Stain 6134 to 500 milliliters of the ball clay terra sigillata. For a rutile slip, I add 20 grams of rutile to 100 milliliters ball clay terra sigillata.

The “Napper Bowl” shown here is a salt/soda fired stoneware piece that was thrown upside down and a slab applied to the base once the clay has set up enough to support itself. The rim is then finished once it is leather hard using a SurformTM (found in hardware stores) and a metal rib, then damp sponged. To glaze the piece was initially sprayed with a Helmer Kaolin slip (80% Helmer Kaolin and 20% Neheline Syenite). Then, using a sponge brush, the rutile terra sig rectangles are alternated with the Ruggles and Rankin green/blue slip mixed with equal parts of the rutile terra sig.  Each rectangle is then outlined with the 6134 Mason stain in terra sig. Finally the Andrew Wong Luster glaze is sprayed on the inside of the piece.

 

 

To learn more about Cathi Jefferson or to see more images of her work, please visit www.cathijefferson.com.

 

 

Comments
  • Cathi: Is the Andrew Wong Luster glaze food safe?

  • The following comment by the Author is interesting
    “Not only does salt glazing seal the ware,….. ”
    As the only active fluxing agent to react with clay in this procss, Sodium is notorious for confering a high Coefficient of Expansion to a vapour glazed surface. Sodium also displaces Potassium from clay and any slips that are applied to the surface. This leads to crazing. When ware is not well vitrified it will seep if liquids are stored in salt glazed containers for an extended period of time. I have found this to happen with fortified wines
    Ivor Lewis.

  • I am surprised by this salt and soda fire fashion in the states, It’s very polluting for the atmosphere
    As ceramists we already use a lot of energy to create, why not go down to cone six at least?

    Maybe it’s nostalgia, the lost paradise?

    Please explain, I’m swedish and live in France

    Mackie Kindal

  • A lot of effort and imagination behind the work to create dalt glazing. Since salt vaporizes and seals the serface and get inter locked with clay surface, I dont see any food safety issue. Good work and tips.

  • I was downloading the whole article. It addresses the environmental issues mentioned above in depth. It seems that it is not as bad for the environment as thought.

  • What do you mean Didi by ‘it seems not as bad’..etc I was taught here in Belgium that salt vapours were extremely poisenous and therefore forbidden to use in a buildup area.

  • Yes Didi, develop please… is it dangerous or not for the atmosphere?
    Or maybe we could give ourselves a good conscience, comparing to the pollution of big industries this is nothing?????

  • Sea water contains salt and the splashes of water (created out of tides waves)send millions of tons of tiny salt laden water droplets in the air which is carried away by the wind to the habitations. People inhale that salted air day in and day out without any side effect. Nature is a great chemitry of neutralization. Nature tries to neutrile every reaction. If a few hundred artisans are making use of soda/salt firing is not going to effect the environment. Its the big factories which emit acidic fumes in the air 24/7 do effect. Do not try to kill the creativity. PLEASE!

  • i’m not trying to kill ……
    let’s forget about fumes and vapours , and toxicity and be happy and creative
    We’ll never get out of here alive anyhow… quote Jim Morrison resting in Paris , cimétière de Pere Lachaise.

  • The cigerrete smokers (who are) making innocent others a “passive smokers”, are more harful than a handful of creative artists. Have you ever compaigned against those unmindful sokers, Maxkie?

  • Don’t know what a chill pill is and it is not about salt vapours we have to worry about. it is the chlore (CL) which is dangerous whether you’re creative or not. With greetings from Belgium.

  • Well the chill pill is that US is far away from Belgium. So the chlorides from a creative work will not going that far. Secondly Soda (Sodium Corponate is being used and not the Sodium Chaloride.

    I hope this double pill will bring about a chill.

  • Cathi – Love your work. I’ll try and come to visit your gallery/studio sometime when I’m down island. I’m curious about the rutile terra sig. 20 grams of rutile to 10 ml of slip sounds way wrong. Is it a typo?

  • Back in 1999, Fresno City College had build a Soda kiln, in the middle of campus no less. After some reseach we would that Soda firing is more hardful then salt firing. One of the universities had done a study to find that the chalordie given off from the salt kiln was actually less then teh chaloride vapors from the campus swiming pool.
    Now i dont know about you, but i dont fire a salt kiln as many times as the number of pools that exsit giving off choliride 365 days a year……Just something to think about. Sorry wish I could remember were the study came from.

  • Hi Everyone,

    Anne – you’re are so right about the ‘typo’ – it’s 20 grams rutile in 100 ml terra sigiallata! Thanks for picking up on that and letting others know as well. If you’re on Vancouver Island please do come visit. Everyone, please do come visit. I have a lovely studio and gallery on the Cowichan River near Duncan. It’s a pretty place with lots of forest trails along a truly beautiful river.

    As someone who considers themself to be very environmentally conscious, mindfully using only safe materials and practices I am so tired at the lack of knowledge of educators that are still fear mongering about salt firing! In 1997, Wil Shryndaruk did some amazing research to finally put all this wrong information to rest and always recommend that everyone read it. It was published in Ceramics Technical No. 5, 1997, titled ‘Taking the Sin Out of Salt’. Also had the good fortune to have someone doing they’re thesis on emissions coming out of a kiln during firing test what was actually happening. Just to put the record straight – it’s salt coming out of the chimney, not any poisonous gas. The fact that I use a fossil fuel to fire my kiln emits emissions, like driving a car, so I try to be as effecient as possible for the 12 to 14 times that I fire my kiln every year. I hope that this helps move us past these outdated misconceptions and move on to the amazing surfaces produced with salt firing and it’s limitless opportunities.
    Wishing everyone all much joy and creativity.
    Cathi Jefferson

  • What is this thing about saltout of the chimney ? When Cleve and I were firing a salt load on Staten Is., I went home on the ferry and the whole bay of water was closely covered with cloud of HCl, hydrocloric acid, the result of salt molecule splitting with water. I know that we digest with HCl. but breathing it ain’t so ‘hot’!!! That’s why years ago we were very nervous about firing with SALT !!! However I hear that some chemist people are finding out more about the safety of this type of firing. Let’s hear some FACTS!!!

  • For a definitive account of an investigation into the composition of the effluent gases leaving a salt glaze kiln (feedstock Sodium Chloride) access:-

    “The ninety-sixth report of the Alkali and Chemical Works in England and Wales Covering the year 1959 by the Chief Inspector”

    See page 46 for an entry relating to Salt Glaze Works. The range of elements identified in kiln effluent will amaze you.

    See also :-
    “Final Report of the Joint Salt Glazed Ware Air Pollution Working Party. 1960” A Confidential report for the British Ceramic Research Association. Director of Research N. F. Astbury, M.A, Sc.D, F.I. Ceram.
    On page 2 it is stated that almost equal amounts of Sodium Chloride and Potassium Chloride were detected in kiln effluent emitted.

    I would also refer readers to L.E. Barringer 1902 , American Ceramic Society. Early volumes of the Society contain a wealth of practical information and research relating to Salt Glaze up to 1943

    The article in Ceramic Technical No 5 by Wil Shynkaruk makes assumptions. Had he or his colleague done their homework they would first have tested their hypotheses of the chemistry they choose to use by calculating the thermodynamic properties of the reactants and their presumed products. They would also have also have incorporated a Control in their investigation that sampled the atmosphere after it had been heated to temperature but before it made contact with any form of silica bearing substances.

  • I loved your video, love your work and again, thank you for sharing your amazingly smooth brushwork & glazing techniques. I never tire of watching other potters work and really enjoy the dialogues that each one of us generates when we show how we do what we do.
    I’ve been a potter for a few decades and have also taught ceramics but still feel that there’s so much to learn about the many techniques, especially the ones I admire but haven’t had the facilities to work within for them like soda and salt glazing. But you just can’t get those gorgeous surface results without atmospheric glazing, and lucky are those who can do so creatively & safely as having a studio/set up for that type of firing isn’t easy.
    Back in 2002 I made a huge decision to quit my job, pack up and move from Asia to Australia so that I could set up my own studio. It’s been a long road and now, 7yrs on, I’ve got my own space. . . and now I get to spend another seven getting “to know” my new-2nd-hand gas kiln. Sadly, I live too close to other homes to work with salt glazing or wood firing but the dream is still there to do so. In the meanwhile, as long as we’re conscious of our surroundings and where we are for atmospheric firings, then go for it! There have been many significant studies regarding the safety issues of salt firings, as mentioned by Cathy and a few other potters in this forum, that point out the best ways to fire using salt. I’m sure many potters who do so take the right measures to fire safely and keep possible emissions low.

    Kudos to those of you who are so fortunate to be able to do so. Enjoy and thanks for what you do.

  • Cathi- Your pots are AMAZING!! Have you moved?

  • I’ve always understood that hydrochloric acid as an airborn gas is one of the byproducts of a salt firing. There is no way any amount of that can be safe for the environment. There has to be a better way to create beautiful surfaces on clay.

  • I get good responses by using a high Sodium Felspar. Brilliant glazes that mimic old fashioned Lead glazes.
    I have yet to read experimatal evidence validating a hypothesis that Hydrogen Chloride is generated when Sodium chloride is introduced into a Salt Glazing Kiln.
    Hydrochloric acid can be created when some metallic chlorides dissolve in Water. Ferric chloride is a good example. It is used as an etching agent during the manufacture of Printed Circuits.

  • i cant speak enghlish but you are very good and usefull

  • Thanks for a job well done, the rate at which you are impacting life is amazing. What a good job for this generation and the generation yet unborn. You are already making your marks in the sand of time. May the Almighty God bless and enrich you to do more. thanks

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