Clay Slip Processing
Cara Domscheit
3rd year, Bachelor Interior Architecture & Furniture Design
What is the technique you based your material research on?
I am fascinated by clay as a material and a resource. I wanted to understand it holistically, where it comes from, where it can be found in The Hague, and what are its limits and possibilities. I was particularly interested in processing the material in a more original way, without a kiln and a ready-made glaze.
Terra sigillata (‘sealed earth’) is a type of engobe (clay slip) used since Roman times. It is applied to dry or leather-hard ceramics and, after firing (max. 1080°C), produces a silky, almost dense surface.
If anything went wrong along the way, what did you do?
Observe it in order to learn from it.
Materials:
500g wild/natural clay sourced in The Hague (self harvested)
1l water
2.5g deflocculant
Tools:
Mixer, scale, bucket, sieve, tube, glass cylinder, pot, hotplate
Workshops:
KABK Ceramics
Steps:
Filter clay to remove coarse dirt (mix with a little water, pass through sieve, spread on plasterboard), and let clay dry.
Add water to glass cylinder and mix it with deflocculant (to prevent the colloidal particles from sticking together).
Now add the dried clay, mix well.
The container should be left for 20 hours and not moved.
After 20 hours you will be able to see that 3 layers have formed!
Pour off the middle part with the help of hose/tube. This is the terra sigillata.
The next step is to determine the correct gravity (relative gravity of the terra sigillata in relation to the same volume of water): Weigh 100g of water in a clear plastic cup on a gram scale (remember to tare the scale with cup on it); Mark a line on cup at the meniscus of the water; Empty cup, refilling it with terra sigillata to the meniscus marking, and re-weigh the cup filled with the terra sigillata; The resulting weight should be between 110-120g. Divide this weight by 100 (the weight of the volume of water) to determine the specific gravity. You can also measure the specific gravity with a hydrometer.
If the gravity is too low, you can heat the terra sigillata using a pot and a hotplate. Stir well and measure the gravity again after about 30 min.
This recipe is part of Touching: A Research Method in Art and Design, an exhibition curated by architect and KABK tutor Laura van Santen, featuring the materials and research of students, tutors and workshop instructors from the KABK.
More information on the display, all samples and recipes can be found here.