(Blog post title courtesy of Mr David Binns)
As part of my self-directed project I am looking at methods of colouring clay without using glazes. As neither my bulb shaped vessel nor my mould seemed to want to dry I took a short diversion into slip testing. I tested a number of slip techniques, using Anthony Phillips (1990) Slips and Slipware book. I identified eleven slip decoration techniques from Phillips, and another four to try from Robin Hopper articles.
APPLYING SLIP - I have used slip occasionally in the past, but not to any great extent, and I had not been pleased with the colours or results. So I embarked on my slip adventures with quite low expectations. The first thing I learned is that using slip is not as easy as I remembered. I had made a small maquette, so I thought I would just dip it in black slip and then add a white zig- zagged band two-thirds of the way up. So I dipped it holding the base. I quickly discovered that when you have applied wet slip to something, it is hard to put it down without touching the freshly applied slip. If you then knock your piece over before it has dried, it will only add to the disaster. Unlike glaze, slip takes a long time to dry, and you cant cover up the marks once you have made them, nor can you wash it all off and start again. Well, it can only get better from here.
SPRAYING - The first batch of test tiles was made, so in an attempt to avoid the dangers of dipping, pouring and slip trailing I decided to spray the tiles and try some new techniques. I sprayed half the tiles white and half the tiles black. This method gave a lovely surface, keeping the crisp square edges of the tiles, and drying relatively quickly. It also had the benefit of allowing me to spray directly onto a wooden board, so no transfer of work was necessary and less risk of touching the slip. The only disadvantage was that some of the tiles were not perfect, and the texture of the slab roller cloth was visible on one tile. When you spray slip, you need to start with a very smooth unmarked surface. Although this was only a test it taught me a valuable lesson when I sprayed my first bulb form.
RESISTS - The next day was time to add the resists and spray with the second colour. Firstly, wax resist was applied and a white slip sprayed on top. The slip formed bubbles on top of the resist and at the edges. It was a bit tricky to remove it with a sponge. Secondly, the paper resist was used, it would at least be easier to remove – and it was. I stuck this down with water, as per Philips, but as soon as the spray gun hit the tile, the paper resist flew off around the spray booth, slightly wet with slip and threatening to land on the tiles. I made another paper resist, and painted it with wax resist. This stuck to the tile, but also peeled off cleanly after the second layer of slip was applied. Success! (- but only temporary, see update 2.)
UPDATE 1- Dave has since told me that the spray gun can be adjusted at the wall handle to spray with various degrees of vigour).
UPDATE 2 - If you stick the paper onto your final piece with wax resist (on a vertical surface) and then spray it, the wax resist and slip mix together and run, this marks the piece even after firing. Not a success after all.
INLAYS - The two inlay techniques showed promise. The first inlay test was to scratch lines into a black tile and then trail white slip into the resulting groove, to stand proud of the tile, and then be scraped back with a metal kidney. Now this should be done on coloured clay, but somehow I thought it might work on a sprayed layer of black slip. The sprayed slip was too thin to take the scraping and some of the original slip came away too. The effect of the white stripe was great though, and I will try it again on a coloured/stained clay body.
The second inlay technique required a wide band to be carved across the test tile, and then the space to be flooded with contrasting slip. This also worked well, leaving sharp edges to the original slip and a nice clean slip application within the band. It was difficult however to judge the level of the slip, and the level fell as the moisture was absorbed into the tile. Not wanting to ruin the black by scraping back, I left the carved coloured band as it was. I like the accuracy of the carving, and I actually like the feel of the recessed white band of slip.
UPDATE - If you make a bulb shaped pot, inlays are more difficult. If they are inlaid in a flat slab it would be hard to match them in a mould. If you carve into your finished pot, as I did, it is difficult to stop the slip running, even when laying the pot on a cushion. This means lots of scraping and cleaning afterwards. It also takes a long time to dry.
LAMINATION – I tried two techniques, the first one involved pouring black slip onto plaster, then lifting it off and carving pieces from it and rolling them into a tile. This seems to have worked well. The second technique was applique where the black slip pieces stand proud of the tile. The pieces are dropped onto wet slip, or painted with water to attach them. I tried dropping them into wet slip, this caused some contamination, but I was able to scrape it when dry. All tests dried without any cracking, and fired well.
MOCHA DIFFUSION - I have tried this before with a tobacco based mix, and it worked successfully. I am not sure how it could be used in a final piece. I came across a recipe that used cider vinegar and manganese dioxide. It was simple to make up, but it did not seem to branch out as widely or as distinctly as previously. I am not sure whether this was the oxide used, the vinegar mix or the slip. I will try copper or a stain, if I use it again. I have also found a slip recipe that is especially for use with mocha diffusion, so perhaps that will produce a better effect.
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