Clay For Extrusion

[Tom alexander]

I make tiles by extruding thru a dye with my pug mill. Tiles are 1/2 " thick by 2,3,4 or 6" sq.

I've been using clay with a 5 small pent firmness which does not extrude very well ( very slow ).

Before ordering another ton of clay I was hoping someone can suggest a firmness that has worked well for them in the same situation. Thank you in advance.

[clay lover]

What is "a 5 small pent firmness" ?

[Mark C.]

My Laguna softer clay which extrudes well is Pent #6

6 1/4# is the normal now for Laguna Clays

I do not know which company your clay is from-many companys use different pent #s systems.

 

You can also add a sponge full of water to each bag roll it on all 4 sides and in a week its all softer.

Mark

[Guest JBaymore]

Penetrometer number. Measures the "stiffness" and "malebility" of the clay. Relates to the amount of water in the body and the particle distribution. Complicated physics.

 

best,

 

................john

[CarlCravens]

What is "a 5 small pent firmness" ?

 

Short for "penetrometer", a method for testing the firmness of a substance.  Laguna talks about clay firmness and testing here:

 

http://www.lagunaclay.com/clays/guide/characteristics.php

 

(In the caption of the chart, they spell it "pentrometer" but spell it correctly in the text body to the left.)

[alabama]

Hey,

     I judge the stiffness of my clays by two methods.  I wedge all the clays to see if how stiff/dryed out they are.  If it wedges, it only means it

passed one of two tests.  After the unit is wedged, I then make a cone and stand it up on one end.  I take a wire tool and start at the top to see

if I can drag it thru the clay by itself... not by holding it with my thumbs.  If the wire tool pulls the cone over, I add enough water (slice, wet,etc.)

until the wire tool enters and exits the clay on its own.  Then I wedge it all up again before I throw.  Or, when I think its wet enough I might run it thru

the pug mill.  It helps by keeping a certain degree of soft clay inside the pug mixer tube.  Alittle preventative maintenance sort of.

     I pretty much do the same for clay meant for the slab roller even though it can be alittle stiffer.

But that is how I judge the stiffness of clays.....

Hope this helps,

Alabama

[Mark C.]

The Penetrometer number Laguna uses as stock has changed a few times over the years

Its 6 1/4 now -10 years ago it was 7 1/4-they decied in past few years to generally have softer clay as stock.

When I order my 10 tons each year I specify what clay I want at what Pent#

usually 2-3 tons softer (to use later as it firms over time)

the rest is stock.

Just when you thought clay was clay.

Mark

[Guest JBaymore]

-they decied in past few years to generally have softer clay as stock.

 

Hum.... clay is sold by the pound, wet.  X pounds dry materials @ X $ per pound = ???  X pounds of WATER @ Y $ per pound = ??? 

 

Wonder why the change to softer clay......... hummmmmmmmmmmm.......... 

 

best,

 

......................john

[bciskepottery]

 

-they decied in past few years to generally have softer clay as stock.

 

Hum.... clay is sold by the pound, wet.  X pounds dry materials @ X $ per pound = ???  X pounds of WATER @ Y $ per pound = ??? 

 

Wonder why the change to softer clay......... hummmmmmmmmmmm.......... 

 

best,

 

......................john

 

Given the warnings about water shortages in the future, in the not too distant future we may see the day where the water costs more than the raw materials.

 

But, really, you don't think the clay makers would add more water just to increase . . . profits? What happened to clay being dirt cheap. Why, that's Un-American and crony capitalism at it's worse.

[oldlady]

I use little loafers from highwater.  it usually is wonderful to throw right from the bag.  it also works marvelously in the slab roller but when it is soft enough to throw I watch it get a little drier before I press things into the slab after rolling.

 

2 years ago, I got new clay from the florida location.  upon opening the first bag I was met with sopping wet clay that stuck to my hands so much I had to scrape it off before I could do anything else.  when I returned it, I was told that they had decided that florida was hot and needed a wetter clay.  NONSENSE!  fortunately, their headquarters knew of the problem and replaced my clay.

[clay lover]

my only experience with Little Loafers was like trying to throw crème cheese.

[oldlady]

have you seen the John Britt video where he did just that?  made a small bowl, put lox on it and took a bite.

[neilestrick]

 

-they decied in past few years to generally have softer clay as stock.

 

Hum.... clay is sold by the pound, wet.  X pounds dry materials @ X $ per pound = ???  X pounds of WATER @ Y $ per pound = ??? 

 

Wonder why the change to softer clay......... hummmmmmmmmmmm.......... 

 

best,

 

......................john

 

 

When I was the tech for a clay company, I was in charge of quality control on the clay production lines. In a 2000 pound batch, 3 gallons of water made a very noticeable difference in the softness of the clay. We generally adjusted batches by 1-2 gallons of water. So, if they added 3 gallons of water to every batch to increase profits it would be 25 pounds of water. Their clay cost comes to about 18 cents per pound including labor, materials, etc for their most popular clays- low fire whites and cone 6 buffs, the clays used by school programs. So that 25 pounds of clay that was replaced by water would save them $4.50, if the water was free, which it's not but I really don't know how much water costs. The company I worked for sold 4 million pounds of clay in a very busy year, so 2000 batches of clay, totaling $9000 in 'profit' by adding more water to the clay than was necessary. At the company I worked for, the pounds of clay sold in a year almost exactly equaled the total dollars in revenue for the year. 4 million pounds of clay equals $4 million in revenue. $9000 is a pretty small percentage. So it's really not worth it to wet down the clay in an attempt to increase profits. Especially since it would only take a couple of customers to get fed up with the wetness and switch to another supplier to totally wipe out the $9000 in 'profit'. I spend about $6000 a year on clay at my studio. Laguna may be a different story since they are so large. I really don't know how many pounds of clay they produce a year. But with the volume they produce their costs are probably even lower, meaning the percentage of increased profit from adding more water would be even lower. Just my thoughts on the matter.

[Guest JBaymore]

I'll take that extra "$9000.  OK... have to pay for the water... make that $8000 a year in absolutely PURE PROFIT.  On $4 Mil a year...... an extra .2 percent of PROFIT.  Add tht to the regular profit margin...... every little bit helps.

 

Remember the whole legal mess a while back when they found some companies in other industries routinely charging an extra penny on a transaction?  The single user didn't give a crap....... probably did not notice...... but multiply that single cent by enough users... and you have some real money.

 

And how often do folks actually weigh the pugged bags they get........   I started doing that with one clay company and found variation  in the "50 pound" boxes by 1/2 to 1 pound.  Sometimes 1 pound per pug.  Do that for the 4,000,000 lbs. Neil mentioned charging about 35-40 cents a pound..... and that is 0.35 x 4,000,000 = $ 1,400,000.  Nice. 

 

best,

 

.................john

[Mark C.]

I was at an art opening this past winter and was chating with Lagunas John Paccini and he did mention how many tons a day they crancked out -I just recall it was a staggering number.

That said over my career especially since wrist surgery I really do not want to work with FIRM clay anymore . It needs to be firmer for taller forms and extruded handles but all other stuff softer is better for me. I have always ordered about 1/3 of my yearly tons in softer clay as it all hardens over time as the bags are not 100% air tight.

As far as a profit I think many a school has complaned about hard clay  when it was delivered ( I know a few that did) and its harder to soften than firm it.

Laguna for so many years had very firm clay and I know many a potter who disliked that. I have always ordered a mix of penta #s as i like my clay in a few different firmness's.

I have spent so much time softing old clay I hate to think about that wasted time.

One last note stoneware is a snap to soften over porcelain and since I am 99.9% porcealin its easier to firm it that the other way.

Mark

[neilestrick]

I'll take that extra "$9000.  OK... have to pay for the water... make that $8000 a year in absolutely PURE PROFIT.  On $4 Mil a year...... an extra .2 percent of PROFIT.  Add tht to the regular profit margin...... every little bit helps.

 

Remember the whole legal mess a while back when they found some companies in other industries routinely charging an extra penny on a transaction?  The single user didn't give a crap....... probably did not notice...... but multiply that single cent by enough users... and you have some real money.

 

And how often do folks actually weigh the pugged bags they get........   I started doing that with one clay company and found variation  in the "50 pound" boxes by 1/2 to 1 pound.  Sometimes 1 pound per pug.  Do that for the 4,000,000 lbs. Neil mentioned charging about 35-40 cents a pound..... and that is 0.35 x 4,000,000 = $ 1,400,000.  Nice. 

 

best,

 

.................john

 

Yes, every little bit helps. But like I said, $9000 would be wiped out by one unhappy customer, so not worth risk. The one cent per transaction thing wasn't noticed by the customers, so the risk was very very small. But make the clay too wet and everyone notices. Even my boss, who was a greedy as they come and then some, kept on us to make sure we didn't lose customers due to clay quality. Drive off 3 or 4 customers and you're losing money by making the clay too wet. I just don't think it's a big conspiracy like everyone thinks. The bigger issue in clay mixing is that the guys mixing the clay usually aren't potters and don't have a clue just how much the water content can affect us.

 

I think the short bags are a much bigger and very real issue. It isn't nearly as likely to be noticed by the customers and cause them to go to another supplier. The problem lies in the method by which the blocks of clay are measured. They are not cut from the pug by weight, but rather by size. The older mechanical systems use a wheel that runs along the pug and makes a cut with every complete revolution. The newer systems use a laser. But once it's calibrated so that a certain size block equals 25 pounds of clay, they tend to use that same measurement for every clay body since recalibration is a pain, especially on the mechanical systems. But the density of each clay varies, and therefore the size of the block required to make up 25 pounds. When I was production manager, we actually set the cutter to 26 pounds so that the less dense clays would make the weight.

[Guest JBaymore]

$9000 out of 4 million is 0.225 percent profit, not 2%.

 

Look closely... that's what I wrote. 

 

best,

 

................john

[neilestrick]

 

$9000 out of 4 million is 0.225 percent profit, not 2%.

 

Look closely... that's what I wrote. 

 

best,

 

................john

 

 

My bad. I don't have my glasses on! Sorry! I edited it.