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Dani

Adding Colorants To Prepared Slips

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To colour slips, I read that one should add 10 to 15% oxides/colorants to slips, presumably while the ingredients are dry. I am preparing white slip using ^6 white clay cubed and put into water, to apply to ^6 speckled tan clay.

What measuring method should I use to add oxides/colorants? I have various stains and the following: red iron oxide, mangenese carbonate, copper carbonate, cobalt carbonate, nickel carbonate and chrome oxide . As I have added washes of these on top of my matt white and speckled bone glazes, it was obvious some were stronger in color than others.

This plate was done in the early 80s when I was at college but I can't remember how we prepared the slip!

All suggestions are welcome. Thankspost-64467-0-48186400-1484603472_thumb.jpeg

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are the cubes of clay totally dry when you add water?  dry clay and dry colorants can be measured.

 

if you are mixing by the "i wonder if this will work?" method, the way i did it for years, and still do,  add some cobalt carb to some white slip and thoroughly mix it with a stick blender.  a wonderful addition to a glaze kitchen not available back when you did the nice pony plate.  look for some color in the resulting mixture, cobalt is pinkish in the carbonate form so your slip might be a soft pink.  separate it into two containers and add a little more cobalt to one.  that way you will have 2 shades of blue. once it is thouroghly mixed in, run it through a 60 mesh sieve and see how it really smooths out the color and the texture.

 

of the colors you have, the cobalt is the easiest, the strongest and the simplest to work with.  copper will give you a green but many glazes that you put over it will turn the green to grey if the glaze has zinc in it.  if you mix your own, a clear without zinc may actually give you green.  rio is also easy but it will result in a dark or lighter brown depending on quantity added.

 

i do not use nickel, chrome or manganese.  they are not things i want to work with.  some of our very talented and knowledgeable academics might comment on their use.  

 

most of all, have fun.

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You can make slip from moist cubes, just always cut the cubes to the same size, and at least 'close' to the same moisture level.
 
Then count the number of cubes you use to make a batch, or just weigh out an amount.  I tend to count cubes since that is quicker and if the slip is too thin, I can just add a couple of cubes to get it thicker.
 
When you test, measure the amount of 'stuff' you add to the slip batch.  Measure by weight or by teaspoons. Just always use the same size measuring tool.  Keep records for yourself.  Test the batch.  If the color is too strong, add some cubes, if too weak, add some more 'stuff'.  After a short test period, you will get 'close enough' to quit testing and start using the slip to make 'your' pots.  Your recipe can always be: so many units of colorant per 10 cubes of moist clay.  
 
For cobalt blue, I would start at about 2% cobalt carbonate to 100 grams of moist cubes.  Red Iron oxide at same level. 
 
I make slips using naturally colored clay, red clay from my pond, crushed iron ore from the entry road to the pond, other dry clays, etc. following the same strategy.  A moist clay body, some colorant, and add water until it is the consistency I need for the pot I am working on.  After a few tries, the recipe becomes intuitive. 

   
LT

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Marcia asked: "rather than using cubes which may be difficult to guesstimate, why don't you just use a slip recipe?"
 
My answer:  
Because I usually make my slip from the clay body I am using, only need enough to decorate a few pots, and the need to add slip is a 'spur of the moment' decision.  I have learned by trial and error how much 'stuff' to add to a 'chunk' of clay to make enough slip to decorate three tea bowls and a vase. I only make a cup full at a time.  Since I am using the clay body of the pot there is no problem of 'fit'. 
 
If I were doing production work where every pot had to look like every other pot, I would make a big bucket of recipied slip, use enough to make three pots, become bored with the whole sheebang, and go read a chemistry book. 
 
LT

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I just made up a half bucket of white slip using the cube in water method. Mixing it up with the paint mixer attachment on a drill was going to be messy. I got a clear plastic bag, put a hole in the bottom to pass the attachment through and drapped the bag over the bucket. After it was well mixed, I pressed the slip through my only sieve, a number 80, and that was a slow process.

I filled 6 small jars with the slip: one white, three with various amounts of cobalt carbonate and two with two different amounts of copper carbonate. Tomorrow, I'll throw a cylinder and try these slips. Looking forward to seeing the results.

I'm wondering if the process of making the slip might have been easier if I dried out the cubes of clay before adding them to water.

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yes, dani, it is much easier to add water and color to dry clay.  save your trimmings and allow them to dry out.  the shavings from trimming are so easy to keep.  any other dry bits can just be broken into small pieces and allowed to dry.  then you can add colorants by their weights.  you still will not know how much to add but if you continue using slips you will work it out and can duplicate colors later.   if you add an excess of water to the dry, it will work nicely once it sits overnight.  just pour off the excess after allowing it to sit.

 

sounds like you are on your way, congrats!

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I just made up a half bucket of white slip using the cube in water method. Mixing it up with the paint mixer attachment on a drill was going to be messy. I got a clear plastic bag, put a hole in the bottom to pass the attachment through and drapped the bag over the bucket.

I'm wondering if the process of making the slip might have been easier if I dried out the cubes of clay before adding them to water.

 

Hi Dani,

This way works to contain the mess too. Yes on dry clay working a lot easier than moist.

PaintMixer.jpg

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what a great idea, min!   i have never had a problem with slip getting messy but this looks like what i need when i start painting the sheds!  will be mixing several odd lots of white and adding some green.  could be a mess but this suggestion is a good one.

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Here's my mixer. I have used it for preparing slurry from locally dug clay, making paper pulp, and smoothing porcelain recycled slip.

http://community.ceramicartsdaily.org/gallery/image/3737-mixerapart-smcopy/

 

It was made in Montana by a friend and given to me. It's back in Montana. It is over 40 years old. Still works.

 

 

Marcia

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