Friday, July 5, 2013

Masking

I still have some work leftover from last summer that needs to be finished. A couple years ago I finished some functional work by layering underglaze colors over masked sections of the forms. With this technique, the naked clay is visible with distinct edges left by the tape I used to resist the colored underglaze. I was really happy with some of my results.

This is my favorite masking tape resist piece.

Also that year, or maybe the year after, I used the same method on pieces thrown using different clay. I don't think the red clay worked as well because there was less color contrast between masked and unmasked areas. I also did several pieces with a layer of underglaze under the mask, but I ran into the same problem of limited contrast. Those pieces are very dark.
I don't like this one as much.

Last summer I threw and prepared some pieces with a fired underglaze layer. I had intended to mask and layer underglaze over these pieces, but I ran out of time in the studio. This week I have begun masking and underglazing several pieces.

Masking tape resist cut-outs applied to purple underglazed bowl (thrown by my mother)

Last time I did this, I used sections of blue painter's tape cut with a knife to mask the underglaze. This works well, but certain types of shapes are easiest to make and round or thin shapes are a little harder to work with. In my experience the masking tape really needs to be applied to fired clay or underglaze. If I try to apply it to unfired clay, glaze or underglaze, the tape sticks to the powdery top layer and comes off or at least peels up at the edges.

Red and yellow underglaze applied over blue painter's tape resists on my mother's other bowl

This technique works reasonably well on fired work and usually the tape stays down with little wrinkling or gaping. Where it does start to come away from the piece, the top layer of underglaze sneaks underneath the edge of the tape, leaving an irregular edge or bubble of color intruding into the masked area. Anyone who has ever  painted wall or trim in a house using painter's tape knows about the irregular gaps or bits of paint that sneak past the tape edge (and make perfectionists seethe). 

masking tape resist removed, leaving slightly rough edges

The little drips and irregular edges on my functional work can be scratched away with a knife. I also sometimes blend them away with a clean wet brush with stiff bristles. Cleaning up the edges is annoying, but not unmanageable and yields nicer edges.

resist lines cleaned up after masking tape was removed 

Last summer my husband brought me some thin blue tape, like the kind used for car detailing. In my studio cleaning frenzy this year before the home tour, I seem to have lost the tape. I was able to find some thin yellow masking tape and have been using that. The yellow tape doesn't seem to stay down quite as nicely and the blue, but it is working reasonably well.

thin masking tape applied, awaiting second layer of underglaze

The thin tape naturally yields a different style of design compared to the cut sections of tape. On several pieces I simply started wrapping the tape around the piece, allowing it to react to the form of the vessel or altering the angle slightly. After the tape had crossed several times, I painted underglaze over the fired underglaze and tape edges. On several pieces I applied two colors of underglaze onto the tape layer with colors alternating based on the sections delineated by the tape lines.

underglaze applied over masking tape lines

Peeling away the tape after the underglaze has dried is pretty easy. Once I pick up a corner of the tape with an end of a knife, I can peel most of the tape line off in one continuous motion, leaving the based underglaze color exposed where the tape had been. In contrast, peeling off the cut sections of blue tape means picking at the corner of each individual shape and peeling each little bit of tape away individually.

removing masking tape resist

I've been working on several different color combinations this week and all have two to three coats of underglaze over top of the tape and fired underglaze layer. Unfortunately the fired work from last year was done on different clays and may have been fired to different temperatures. At any rate, some of the pieces absorbed the fresh underglaze better than others. It may turn out that the top layers of some of the underglazes, after firing, are semi-transparent or streaky. There isn't much I can do at this point, other than be careful about my application and clean up.

resist lines removed, underglazed piece awaiting glaze application

Streakiness risks aside, I knew that the masking tape methods would work reasonably well. However, earlier this year I purchased a couple different kinds of liquid masking products from a clay supplier. I wanted to see if these products would work better than the masking tape. I do a lot of layering of glazes on all my work and I thought it might be nice to use these products to help cut down on the quantity of firings I use to set various layers of underglaze color. I also thought these material might be easier to manipulate than the tapes.

Laguna Latex Resist and Duncan "Mask 'n Peel"
So far I am not impressed with the products, though I have only done a few tests using these products in concert with other masking techniques. I suspect they are intended for more direct application. Apparently they are also intended for people who cannot smell. 

blue plate with yellow and red label-masked underglaze

In an attempt to to test the materials, I applied some sticky labels to the interior of an underglazed and fired plate. The labels can be used just like the masking tape as resist with a standardized size. I applied some of each of the commercial resists to the top of the labels and the surrounding plate. My idea was that I could then peel off the labels and glaze the gaps inside the resist lines. I was trying to resist the resist. Unfortunately both types of commercial resist stuck strongly to the paper and peeled off without any give. 

a wad of labels and stinky toxic resists

I suppose I used the commercial resists in an inappropriate way. Eventually I'll use it to freehand some decorations, but I do not like the material so far and it seems excessively pungent and toxic for how I like to work. One of the resists, the larger container from Laguna, comes with dire warnings about toxicity. Potters are urged to wear gloves and a respirator and wash their hands thoroughly after use. The Duncan resist does not come with such warnings, but both resists smelled terrible. I wore a respirator for both (after I figured out how awful they were). Both resists also were hard on my brushes. They did peel off the clay well, unfortunately ruining all my planning.

beginning to peel off Mod Podge masking layer
However, I still wanted to use my "resist the resist" method to decorate the plate, so I tried another resist material that I happened to have on hand, one that didn't smell so bad and that isn't quite so toxic. This second material worked wonderfully as a resist:

my new resist
To get the Mod Podge to work as resist, I simply painted a thick layer of of it over my (newly applied) paper labels. I needed to score some of the labels to get them to to peel off without taking the Mod Podge with them, but they peeled off reasonably well and the Mod Podge stayed put. After I painted on the underglazes, the Mod Podge peeled off more easily than the masking tape did. The only trouble I had with the Mod Podge resist was as the edges where I had applied it too thinly. I probably could have painted an extra layer in these areas to help pull it off the plate but instead I decided to fire the plate an extra time before applying a clear glaze to the surface of the plate (just to be sure). As an added bonus, I know from experience that Mod Podge washed out of brushes even if you forget to wash them right away.

Mod Podge resist mask being peeled off (and taking the underglaze with it)

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