colored slips

[Elke Levine]

I am trying to create some colored porcelain slips. When i mixed yellow core oxide into into thinned porcelain clay it comes out brown after firing it to cone 6. I tried the same with A Berry mason stain and it come out grey. How can I achieve a yellow core or berry color slip that does not change color at cone 6.

[Min]

Hi Elke and welcome to the forum. When you say "yellow core oxide" are you meaning yellow iron oxide? Not sure what yellow core oxide is but yellow iron oxide could give you brown.  Also, are you using a glaze over the mason stain and which stain is it?  If you look at the reference chart information that Mason supplies find the stain you are using and then read the reference notes for that stain. For example for chrome/tin pinks, crimsons and coral stains the glaze needs to have zero zinc and high amount of calcium in order for the stain to work and not change colour. 

[neilestrick]

I think you mean yellow ochre? That's a form of iron oxide, so it'll go brown. If you want yellow, you'll need to use a yellow stain. Like Min said, many stains require a certain chemistry for them to keep their color, and some will only work at certain temperatures. To stain a slip you'll need a lot more stain than you would use for a glaze. Generally you need 10-20%.

[tutko]

I use warm brown stoneware with my students and want to incorporate a project that uses colored slip.  Is there a specific type of mason stain I should get that would work best with the clay we use in class?  

[Callie Beller Diesel]

I just pulled some coloured decorating slip tests out of the kiln this week, so I can share some results about a pink. This is 5% red Mason stain 6021 in a white slip over a red clay body. Half the tile is glazed, half the tile is not. The glaze does contain zinc, but there's some pinholes.  The pinholes are only over the slip on this test, not on any of the other slips I tested.  As a next step, I might try to do a line blend to see if I can get a good colour out of a smaller amount of the stain, especially because that one is pretty expensive. I also wonder if a lower amount of stain would off gas less, and not leave the pinholes.

[neilestrick]

12 minutes ago, tutko said:

I use warm brown stoneware with my students and want to incorporate a project that uses colored slip.  Is there a specific type of mason stain I should get that would work best with the clay we use in class?  

To make the colored slip you'll want to use a smooth white clay as the base. Any clay body that fires to the same temp and has the same shrinkage rate as your class clay will work.

[Min]

@Callie Beller Diesel, don't think it will be the stain off gassing as stains have already been fired and sintered. Try adding 2% zircopax to the slip, probably be able to use less stain then. I know it seems counterintuitive but it helps to  intensify the colour of Cd inclusion stains. Since the Mason 6021 is a cadmium inclusion stain the zinc is fine in the glaze recipe and won't effect the colour.