The search for all elusive plasticity in clay is often shrouded in mystery. In graduate school I tried everything. Soap, beer, piss (never do this by the way) time…everything. Generally speaking the best method was to work in some old chunks of clay into the recycle mix. add some softened bentonite (I’ll cover this later) and wait about three weeks. At least three weeks.
Bacteria it is thought leads to the possibility of increased wetting. and incredibly wet clay is incredibly dense and plastic. Density and plasticity improve just about every aspect of building and throwing. No matter if you are working with a stoneware,porcelain, or earthenware – the plastic clay body is the strongest and best to work with. There is no doubt.
I read an article recently that indicated slight acidity aided in plasticity. Slightly acidic water aids in the wetting action of the clay which renders a maximum plasticity of any dry mixed clay body in about 72 hours. three days is shorter than three weeks. This is the kind of math that an artist can understand. In most part of the country the water is basic. So slightly acidifying the water before mixing in your dry ingredients will yield a throwable clay body in just a few days. I’m in.
Lacking any PH strips I chose to experiment a bit. For a 10 gallons of water I added 2 tbsp of muriatic acid. Note: this is available at your local hardware store. It is used to clean cement. It’s really dangerous stuff. It will blind you so wear goggles and be safe when handling it! The first clay we mixed was the original porcelain: with a few additions:
25 ball clay
25 custer feldspar
I like to simplify my recipes whenever possible. After weighing , I discovered that if I used a 3 gallon bucket as 1 part, It worked out to 1 part of each to 1/2 part of silica. This simplification worked great although the Custer feldspar is a bit dense – allowing for another part. so I chose to make that 5th part Pyrax, Grolleg, PV clay, in about equal amounts.
The pyrax aids in mullite formation.
Golleg aids in working characteristics and plasticity
PV (plastic vitrox) is added for plasticity
So, the clay is converted to:
2 parts ball clay
1 part silica
2 parts custer feldspar
2 parts epk (or georgia or tile 6)
1/3 part grolleg
1/3 part pyrax (or spodumene)
1/3 part PV clay.
The addition of Muriatic acid was definitely beneficial as an aid to plasticity. It worked great! Since that time I acidify the water every time we mix new batches of clay. No matter the mix – be it stoneware, earthenware or porcelain – by all means you should definitely work with a PH of about 6.5 is considered to be the most effective for the proper wetting (and therefore plasticity) of your clay.