My Clay and Processing

I always wanted to make my own clay for throwing, but felt I needed to gain throwing skills before starting to make clay.   Simon Leach made it look simple in two videos ( https://youtu.be/odUM7Rwuv8M and https://youtu.be/sJkTjq5zLws ).   I tried to make my own clay when I installed the new kiln in 2016, but the bowl turned into a collapsed glob on a new kiln shelf.  Not good.  I turned to Wendt Pottery of Lewiston, Idaho to learn how to throw using his bagged clay.  Wendt is a local commercial potter with over 40 years experience.  He mines his own clay locally and has the permits and processing equipment.  Wendt's bagged clay is a pseudo-porcelain clay fired cone 10.  

Thoughts and Hacks when working with dug clay

1. Changing the melting point of native dug clay by adding feldspar may have prevented the first bowl from melting down.

2. Lowing firing temperature would have also prevented meltdown of the dug clay. 

3. There was a lot of grog in the dug clay and the clay did not stick together very well so maybe need to extract less from the bottom of bucket.   

Pugger pugmill vpm-7ss

I purchased a Pugger stainless steel pugmill plus stand from BigCeramicstore.com in December 2017.  It was their small pugmill with a 14 lb mixing chamber that allows mixing, deairing, and pugging.  Pugger makes a 25 lb mixing chamber but I felt 14 lbs was a better match for my production and need for small batches.  For me, the bagged clay was not soft enough to throw after a couple of weeks storage.  Most potters either add water or moist clay and mix by hand wedging to freshen bagged clay.  A hand\wrist injury of my past made hand wedging difficult so a mechanical solution was the next logical step and has turned into a good investment. 

The Pugger has change my throwing to taller and thinner.  Yes, softer clay helped, but I am taking greater risks knowing a failure can easily be recycled the next time I mix.  I found the round log was perfect for centering and no longer form balls for throwing.  Just cut and center on wheel.   

After consulting with Wendt Pottery the clay recipe in image below was tested in the pugmill.  I found it to be identical to Wendt's clay in throwing and firing in the kiln.  

In 2023,  The mine processing Custer Feldspar declared bankruptcy.  Laguna Clay Company recommended Vardhman (55#) potassium feldspar.  

Shipping is the real cost of raw material for clay.  Estimated shipping cost for raw material to make 23 batches ranged from $150 to $300 in 2018.  My solution was to freight a year's supply (620 lbs) of both raw materials and glaze directly from Laguna Clay Company factory in southern California for a cost of $175.   Wendt pottery indicated he shipped from the Clay Arts center in Tacoma, Washington because the shipping costs were low.  In 2019, my inquires showed the shipping costs were lower from the Clay Arts Center but they charged more for the raw material.  On an 850 lb order from Clay Arts Center was $35 less than shipping directly from Laguna Clay Company.  It reduced the cost of raw materials by $0.03 per lb of pottery clay.   In the fall 2019, Clay Arts Center website price was $64 more before shipping and they never provided a quote for shipping.  I ordered from Laguna.  The cost of shipping in 2024 is up by 3X, but materials plus shipping costs are still less than $1/lb.    

Thoughts on working with dry clay with Pugger mill.

1. A full batch on the 14 lb pugmill will yield 12 to 14 lbs wet clay.  

2. Small flour scoop works great for scooping dry clay into the pug mill.

3. An 18 inch piece of hand rail works great for tamping down clay in the pug mill.  Alternative could be a 2 by 2 inch with edges rounded.

4. Mix should start immediately after pugging out the last batch. 

   1. Dry clay mix is added 5-6 scoops plus 3 cups water then repeat and add a top plug of wet clay.  Close lid and leave for 6 to 24 hours without mixing.  Next day mix 5 minutes. 

   2. Open mill and tamp  down.  Add 4 cups dry clay mix and 2 more cups water and top plug of wet clay.  Mix 5 minutes.  

   3. Open mill and tamp down.  Add 3 cups dry clay mix and 1 more cup water and top plug of wet clay.  Mix 5 minutes.

   4. Pug clay without vacuum cutting pugs into 2 inch sections.  

   5. Add 2 of the wettest pugs back into the hopper the mix for 15 to 30 seconds.  

   6. Add 2 cups dry clay mix if the wettest pugs are slimy.  Quantity of dry clay is based on how the slim factor of the wettest pugs.  

   7. Add remaining pugs with 5 to 6 minutes mix times.  

   8. Check clay consistency in vacuum chamber

      1. Needs more dry if ribbon coming from mixing chamber > 1 inch wide.

      2. Needs more water if ribbon coming from mixing chamber < 1/2 inch wide or chips 

      3. Just right if ribbon coming from mixing chamber is between 1/2 and 3/4 inches wide. 

   9. If you added dry clay then you will need to mix and pug again until you do not add dry clay. 

   10. Final mix should use the vacuum.  Pug out three 2" sections to remove unmixed clay from the nozzle.  Open the mixing chamber and add them back into pugmill.  Reapply vacuum and pug out at full speed.  Negative pressure should be above 23 lbs.  Cut pugs about 6 inches long.

   11. Sometimes the chamber will start to loose pressure when pugging.  Push clay feeder handle down to reseal and vacuum may rebuild.  If it does not and vacuum falls to zero, pug clay out and reintroduce it to the pug mill but do not overfill.  

   12. Quality control.

       1. If log breaks off when extended 5 to 6 inches from nozzle end it is too wet and will need to be repugged with 1 to 1.5 scoops dry clay added.

       2. if log has a dry spot trim out spot or mix and re-pug.

       3.   Lightly squeeze clay as it is pugged.  If big dent too wet.  If no dent too dry.  If slight dent just right.

5. Water used for mixing can come come from the waste water recycle bucket.     

6. If necessary, a few chlorine crystals in the water used to mix clay prevents mold growth.  Most of the time recycled clay water is used fast enough that mold is seldom a problem. 

7. Working with dry batch clay is DUSTY.  It is like working with flour and powder sugar.  Wear a dust mask.

8. Single dry batch clay (14 lb) is perfect for a 5 gallon bucket with lid.  It leaves 1/3 head space and the weight perfect for mixing by rolling the bucket and shaking.  The 14 lb amount is enough to make 1.5 batches of wet clay in the pug mill.  I use a 5 gallon metal shipping bucket with a lever lock lid from uline.com.  An alternative can be made with a paint plastic 5 gallon bucket.  

9. Pug clay the day or two before use helps clay set for easier throwing.  

Clay recycling with a pugmill

The addition of a pugmill changed recycling to a direct add into my normal mixing stream.  Pugger mills are built to accept all forms of raw clay from powder to recycled clay.   My recycled clay includes both trimmings and wheel and water bucket waste.   The water bucket settles overnight and  siphoned off water using the tubing described in Glazing section.  The remaining slip is used to add moisture to that days pugmill mix of fresh clay.   The pugmill recycling process works so well I have re-purposed the equipment used for traditional recycling. 

My thoughts and Hacks.   

1. The water bucket from wheel is stirred and poured into a settling bucket (2 gallon paint bucket) daily.  Let settling bucket set overnight. Siphon off water using the tubing described in Glazing section.  The water from waste bucket is used to water flower bed and compost bin.  When settling bucket has 1.25 inches clay in bottom use it to hydrate the clay in the pug mill.