Do oxide washes leach when applied under or over glaze layers?

[Beebop]

Hi all! 

I’m interested in trying out oxide washes below and/or on top of glaze layers, but wondering in general, how much can you expect oxide wash layers to interact with glaze layers? 

I am familiar with the oxide colorant limits recommended for making safe and stable glazes, Hasselberth and Roy being my go-to reference for that. Obviously a wash or slip falls outside the bounds of a stable glaze because it’s something different, so are they stable when used with glazes? Will oxide washes saturate into a glaze and leach, or do glazes act as a barrier to prevent leaching? Is it possible to apply washes over glazes without there being significant leaching? If I add some frit or slip instead of using only water to the wash, would this help stabilize the colorants in the final product? Would that opacity the final product?

 

My ultimate goal is to create glaze surfaces that are layered, non-homogenous with a lot of visual texture and depth, I thought washes might be a good technique to add to the mix. But when it comes to functional wear, I realize some of what I’m trying to cannot apply, just not sure which side oxide washes fall. 

Thanks!

 

[neilestrick]

If the oxide is on top of a glaze, I wouldn't trust it to be taken in to the glaze to the degree that it would be fully encapsulated in the glaze and be considered food safe. If it is under the glaze it can be totally covered and food safe, however if the oxide is too thick it can saturate the glaze to the point that it's no longer food safe. If you limit the application of the oxide to areas that will not come in contact with food- the outside of bowls and mugs, for example- you don't have to worry about it.

[Callie Beller Diesel]

I came here to say more or less what Neil did. Keep it on non-food contact surfaces.

It would be very difficult to come up with limit formulas for a non-homogeneous mix. If you wanted to put it on a food contact surface, you’d have to somehow make your application consistent, and send it off for testing to make sure.

[Beebop]

thank you both for info! i’m also concerned that if colorant is oversupplied from an oxide wash, that even exterior surfaces not in contact with food might color shift over time due to harsh wash cycles. sounds like i should keep washes thin and below glazes for functional wear and out of contact with food contact surfaces all together. i usually just do single liner glazes on interiors, i’ll just stick with that. thanks! 

[neilestrick]

The simplest way to get color under the glaze is to use commercial underglazes. They're available in just about any color, can be blended to make other colors (to a degree), and can be thinned down and used as a wash.