colouring large batches of porcelain

[Ozon]

Hi, 

 

I have a question regarding mixing of large quantities of porcelain into colour. Like 10 kg of each colour. Would you recommend a pug mill for doing this job? 

[Chris Campbell]

My reply would be two questions ...

How often do you think you would be doing this? A pug mill is a big investment if all you want to do is color some clay once or twice and I am really not convinced it is the best tool for the job.

How many colors? ... Multiple colors means totally cleaning out the mill between each batch ... ugh!

[Marcia Selsor]

I'd mix a few  kgs at a time with a blender and dry it in a plaster mold to the right consistency. I think you'd get a better blend than in a pug mill/

you find a smaller used dough mixer.maybe that would work.

Marcia

[Ozon]

Thank you very much for your replies! 

I would want to mix around 10-20 kg porcelain each 1-2 weeks. Ten kg each in different colours. The reason I'm asking is that I do a lot of other hand work and it affects my wrists and back. I'm afraid if I keep doing all the wedging and mixing of colour by hand over time it will have a negative effect on my health. The other reason is that by hand it is really hard to keep the plasticity of the porcelain and also mix the colour and moist evenly in the clay. 

At the moment I'm drying out the clay into powdered form, mix the stains and re-wet everything and then bring it back into working consistency.  It is very time consuming if I wish to create large batches and it starts to become stressful in finishing off other parts. 

Any suggestions would be really helpful. I have also looking into the dough mixer but it is more useful for small quantities or maybe not?

Many thanks for your help! 

[Bryan Johnson]

For that size batch I like using a stainless steel Peter Pugger VPM 9.   How I prepare the colorant depends on what it is. Some I ball mill, some I blend, some just get put in the PP with water.  Starting with a 25% batch makes a mix that can be added to a white base with 1# adding 1%.  I like using a progression of colors and shades so that what is left in the mixer adds to what I want.  Something like dark blue to light blue to blue green to brown to tan, maybe clean it out and   then yellows to orange.  I run the clay through twice to get the clay in the nozzle mixed in. The vpm 9 leaves about 8#s in the nozzle, about half of which can be extruded before it is mixed with the new color.   I find the density of de-aired clay much better for polished work.  This might be some what dependent on  the clay.  

 

[bciskepottery]

One thing to check out is if you can get your clay dry, not already mixed.  That eliminates the need to dry it out to get a powdered form.  Many clay manufacturers sell their clay dry. 

[Chris Campbell]

I use a commercial size Hobart dough mixer, but these might be more expensive than a pug mill.

One way to make your job easier is to saturate your clay with stain. By that I mean ... if you want 5% mix your batch at 10 or 15% ... it is very easy to knead in the right amount of white clay to bring the % down ... less clay to store and less times you have to make it.

[glazenerd]

Ozon from what you have posted thus far: buying a mixer/pugger may be your best option. I suggest this based on the assumption, that coloring porcelain will be an ongoing mode of operations for your studio. Note I said: mixer/pugger, because there are differences between straight puggers and mixer/puggers. Most all mixing puggers are single auger, and require the machine to be full, including the nozzle; because part of the mixing action requires the back pressure of a completely full chamber. Dual auger mixers work much better, but in the States: dual auger mixers only come in very large capacities. I will add some step by step instructions in the AM because the laptop I am on does not seem to be displaying correctly. I will add them as an edit..sorry. Nerd

Peter Pugger is a great pugger and a mediocre mixer: I have the VPM 20. I have used a Bailey, which does a quicker job of mixing. Regardless, both machines need to be completely full in order to properly mix. The easiest way is to batch mix from a dry blend, as Bruce suggested, If you go this route, add the water to the front of the hopper, not the back: and in one third increments at a time, then mix. You add all the water at once, you will end up with a rotating slim ball at one end, and a brick at the other. Pending the dry blend, roughly 1 1/2 cups of water per 1000 grams of powder. The clay must be at a certain consistency before it will effectively pug out. You can tell when the auger tines leave defined ribbons in the clay as it passes through them.

If you start with premix, load the machine until it is full. Then pug out about 2 lbs, which is roughly a 3" log. Slurry down the two pounds with1-2 cups of water and add your stain to that. Then add 1/4th of that mix at a time and mix, add 1/4 and mix..etc etc. Let the machine run for several minutes before adding: remember it is only making 12-15 revolutions per minute. Once you get the mixing chamber uniformly mixed, you have to come back and add dry powder to get it back to the proper consistency.

You can either mix your own dry powder from scratch: or save all your trimmings as you go and pulverize them back to powder. In essence, you will have to get into the routine of saving or making powdered clay from your premade. I keep a separate bucket to keep all the cream off my hands and trimmings, and have a cheap blender to pulverize it in.  I mix my own clay blends from powder, so my system is somewhat different than yours.

Once you have blended everything, pug out about 15" to clear the nozzle, and add it back into the chamber. You will have to repeat this several times until everything is uniform in color.

Color development: moist clay typically has 25% moisture content. ( + or -) So weigh out 125 gram blocks; which will be close to 100 grams when dry. Slurry that down to a thin peanut butter consistency with water. Add your stain based on percentage per 100 grams of dry powder. Then spread on a plaster batt to dry it back down to its original moisture content. By using these 100 grams test samples, you can cheaply figure out your color pallete, and figure out what percentages of stain/s to add to your large mixing batches.

NOTE TO PUGGER MAKERS: the first company that comes out with a 25 or 50 pound dual auger pugger/ MIXER will out sell your competition. The only dual auger mixer/pugger currently holds 125 lbs. The smaller dual augers pug only, they do not mix. So someone needs to make an intermediate size dual auger mixer/pugger with de-airing compliance.