Shrinkage, sure

[CactusPots]

I throw on hydrocal bats and really like them.  Hydrocal, as you may know, is like plaster, but more durable and is less absorptive.  I like to throw a thick bottom and trim my feet in.  Scraps go to the pugmill, so there's no waste.  What I find interesting is that different clays release from the bats at different dryness.  The quickest is Amador by Laguna.  It will freely release when still soft.  My other main clay is Soldate 60.  Not quite so soft, but still good.  My recycle, though, can hold tight until it's almost full leather hard.  I really have never gotten a good understanding or explanation about this.  Any ideas?  

[liambesaw]

Not sure. I throw on Masonite bats and they release both clays I use when leather hard (thank God).  I try not to trim on forms like mugs so it's a real time saver, but on forms I do trim, like bowls and vases, it's really nice because as soon as they release I can trim and it's perfect

[glazenerd]

1. Water content of the clay..the obvious variable.

2. % of ball clay or other plasticizers. These hold water longer than kaolin, dry slower.

3. Sodium vs othe fluxes: sodium accelerates drying..hydrophobic material.

 

[CactusPots]

Thanks for the info glazenerd.  A couple of questions

1.  My recycle is generally wetter than the commercial stuff.  I like it that way because I can easily center larger.  The release point for the clay on the recycle is noticeably stiffer than the commercial clays.  I can see a longer release time, but still having a grip on the bat when the trimmings are falling apart?

2.  This was my initial thought and I tried adding ball clay to the recycle mix, but this resulted in a short clay.  My extrusion from the pugmill is about 20 lbs.  Can you recommend an amount of ball clay to add?

3.  Does commercial high fire clay contain additional fluxes?  I haven't really studied clay composition the way I have glazes since I don't scratch mix clay.  Since I have the pugmill, I've become more interested.  I haven't noticed anything I would think of as a flux in any clay recipe I've seen.

I don't run a wire through the bottom of pots smaller than say 6 lbs.  I trim a lot as it is and want as much as possible on the pot.  I count on the bats releasing.

[Mark C.]

I would not add any extra ball clay

Its more important to add your slop or what is known as the fines -those small particles in your splash pan and settled water bucket. A few drops of vinagar can help as well.

You are in luck with Almador as its one of the cheaper clays Laguna offers and works well in reduction atmospheres .

You could also make some #1 pottery plaster bats for your sticky clays as it sucks water out better.

 

[CactusPots]

My recycle, being half (more or less) between Amador and Soldate 60 is really a nice clay.  It's in demand when I share it with other potters.  My product doesn't require Bmix, or any other fine clay.  I haven't touched porcelain in years.  I have some recycle that has a small amount of Peter King in it. 
Even better. 

[glazenerd]

11 hours ago, CactusPots said:

Thanks for the info glazenerd.  A couple of questions

1.  My recycle is generally wetter than the commercial stuff.  I like it that way because I can easily center larger.  The release point for the clay on the recycle is noticeably stiffer than the commercial clays.  I can see a longer release time, but still having a grip on the bat when the trimmings are falling apart? you already stated that your recycle is noticeably wetter: which explains the longer release time. The base of your pieces are notably thicker, and  not exposed to air like trimmings.

2.  This was my initial thought and I tried adding ball clay to the recycle mix, but this resulted in a short clay.  My extrusion from the pugmill is about 20 lbs.  Can you recommend an amount of ball clay to add? Ball clay should not result in shorter clay unless unless  you are adding a low plasticity ball clay. Given the color of Soldate: I would be using FHC (foundry hills cream) which is high plasticity, but also slightly higher in iron.  For 20lbs: 80% FHC, 10% silica! and 10% feldspar. 1 cup of mix per 20 lbs. adding a fix it mix is highly dependent on how much water and pressure you use when throwing. If you produce a lot of cream when throwing, then you need to add the mix as outlined.

3.  Does commercial high fire clay contain additional fluxes?  I haven't really studied clay composition the way I have glazes since I don't scratch mix clay.  Since I have the pugmill, I've become more interested.  I haven't noticed anything I would think of as a flux in any clay recipe I've seen. The higher the cone fire, the less flux required. A cone 10 porcelain has 25% flux! cone 6- 30%, and cone 5- 34%. Potassium spar works better in stoneware bodies.

I don't run a wire through the bottom of pots smaller than say 6 lbs.  I trim a lot as it is and want as much as possible on the pot.  I count on the bats releasing.