Pit / Barrel firing
Terra Sigiallata
Making Terra Sig
Well I thought Saggar Firing was exciting!
I've just started experimenting with Barrel Firing above ground as opposed to pit firing under the ground to start with and found it very interesting - lots of room for experimentation here. I am using a 44 gallon drum cut in half with holes drilled around the bottom of the side of the drum for air circulation. I sit the drum on bricks with a couple of holes in the bottom underneath the drum again for air circulation. This seems to work well so far.
Artwork must be made of strong stoneware clay with a tolerance for high temperatures as it will be in contact with direct flame throughout the process. This type of firing allows the artist more direct involvement during the whole process and more opportunity to influence the outcome of your finished piece to some degree. The pieces are placed on a bed of sawdust, wood shavings and twigs and scrunched up newspaper. Now for the influencing factor, depending on what outcome you desire, you add other materials such as salts, carbonates, oxides, metals, organic matter etc placed around and in close proximity to the surface of the pots.
Now for the building of the fire, stacking more twigs and paper on top, then the heavier wood
then light the fire. You need to get the fire roaring with flames, fanning from time to time.
Wearing appropriate clothing is essential as safety
around an open fire is paramount. The heat can be intense. Always have a hose at the ready for safety. You need to stoke and keep throwing timber on the fire and keep it roaring for around about an hour. This should be ample time for the fire to reach the desired temperature, then you can let it settle till it dies down to ash and cinders then put a metal sheet over the barrel 3/4 covering it and leave it. This is when the salts and chemicals and organic matter start to react with each other and work their magic. After about 8 hours (perhaps even a little longer from a safety point of view), it should just be cool ash and ready to take out your pieces. Do this with gloves as the pieces may still be a little warm. Time to uncover and see how creative the Fire Gods have been with your magic potion. Make notes - it is important so you can make changes next time to your cocktail of chemicals and organic additives to influence different results, colours and textures.
NOTE: It it critical to get the desired heat, so make a good fire with lots of wood and pack well.
During the above process it is always good and safe practice to wear a mask and appropriate safety gear as you are dealing with salts and chemicals in a toxic state and health and safety is paramount.
Terra Sigiallata is something you are just going to have to experiment with. You have got to understand what it is, how it works, its vulnerabilities, its advantages and or it's disadvantages.
I found it frustrating trying to access on line information on making it, as again there appears to be lots of different recipes and sometimes it is better to make it with the same clay body of the piece you are putting it on. There are short cuts with everything but then end results will always reflect that, so do the hard yards and do it properly, it will be worth your while.
Advantages - (a) Finished piece will polish up with an incredibly shiny surface. Having said that your piece must not have any flaws in it as it will show up every fault.
(b) There is no need for laborious hand burnishing with a stone beforehand, just close the pores of the clay with a metal kidney smoothing the surface before applying Terra Sig. Just after appying Terra Sig, burnish with a piece of soft plastic or cloth, I sometimes use an old stocking.
I also like to use soft cotton gloves when working with Terra Sig or handling work with unfired terra sig on so as not to leave any oil marks from your hands.
Disadvantages - do not let water any where near your piece once it has the Terra Sig on it. When your piece has been fired, do not put water on it to take off the naked raku glaze, let it cool down then just flake it off. I have found once you start playing with Terra Sig, you need to strive for perfection, as mentioned earlier, every flaw will show up in its glossy finished surface.
Special Note - When Naked Rakuing, I
normally start checking my work at
around 700 before taking out - HOWEVER with Terra Sig I very quickly learned you will have to start checking at around 600 onward as you now have a VERY slippery surface which the slip and glaze will possibly want to seperate from earlier - paramount to watch very carefully. This may depend on the slip and glaze recipes of course. Experiment first before applying to your good pieces...it will save the heart ache and disappointment.
NOTE - When applying Terra Sig, use a really good brush, you don't want loose hairs stuck on you piece, it may burn out but it will leave a mark.
Making Terra Sigiallata can be a messy and time consuming exercise. But like anything, if it is worth while, it is worth doing properly. If you can purchase Terra Sig and it works for you - fine, but it is not always available. We can't get it here in West Australia.
When looking for recipes, depending which country you are in you should source ingredients accessible or known to you. i.e. as a defoluclant USA would use "Darvan 7 " which we in AUS would substitute with "Soda Ash" or "Sodium Silicate" or both. (I use a 50/50 mix of both).
Whether you prefer to make a Terra Sig of the same clay body you use for your pieces or make a general one of powdered "ball clay" to begin with I would do both and experiment what works best for you. I found "ball clay" difficult to define the different layers to siphon off as the particles are so fine.
Make only a small manageable quantity to start off with while experimenting.
When you are happy with the results, colours and clays you can make bulk.
NOW for recipes.......hmmm there are
so many different recipes. Best you experiment and see which works best for you. If you are adventurous, go find some clay soil and process yourself. Very time consuming but certainly may be very rewarding. That is my next exciting journey.