Slip casting

Having enjoyed press-moulding various plates and a planter, I thought I would once again avoid throwing and have a go with slip-casting.

First stop, Pottery Crafts.  I now have some Buff earthenware / stoneware slip for bisque firing at  120°C-1280 °C. The fired colour is described as “buff / grey” and it is on the smoother side. The predicted result is something as follows…
160-1205

I expect it will come out on the darker side as the bulk firings at the studio are done at stoneware (i.e., slightly higher temperatures).

I am also armed with some DUNCAN Crystal/Crackle Glazes for firing at 1000-1020°C. I expect these will be too low for the studio so I may need to fish around elsewhere for a kiln. At any rate, I will try them on a sampler.  These are intended to be paint on.  0047139_cr-907-la-fiesta-16oz

The first round of colours are (i) Peppered Raspberry, (ii) La Fiesta, (iii) Waterfall, and (iv)Blueberries. The labels have a useful guide to enable you to make the appropriate choice as to food compatibility and basic firing information.

Capture

Basic Instructions:

1. Stir glaze without disturbing crystals.
2. Apply 2 coats to shelf cone 04 bisque.
3. Mix in Crystals for 3rd coat.
4. Apply crystals sparsely near bottom of the piece to keep crystals from flowing onto kiln shelf.
5. Stilt and fire to shelf cone 06.
6. Clean up with water.

Application is with a brush and is fairly self-explanatory as per the following video


As for the moulds, I have gone for a teapot and mug combo which are quite simple but a bit more exiting then just fat and round.

2 I would love to be able to make my own moulds, but one step at a time…

I would also love to try out some tissue transfers, but have no idea where suppliers are in the UK. Australia appears to have a monopoly, with some limited exportation to the USA… Apparently it is possible to do something similar with DIY screenprinting, but I have no experience at all with screen printing so that would also need to be attempted ab initio.


I thought about doing the whole thing at the studio, pouring, waiting, doing some yoga, more waiting, hair drying it… But I’ve been there before.

Therefore, I assembled everything on my bedroom floor and began there. I grabbed a whisk from the kitchen and mixed up the slip in its gigantic barrel. Needless to say it went everywhere, but at lease I had the foresight to move my rug out the way so cleaning the drips of the wooden floor wasn’t too bad.

Then I disassembled the three moulds. The first and the smallest was the top of the tea pot and was only a two part mould which neatly slotted together. I rubber-banded it in place.

The other two, being the two mugs and the body of the tea pot, were three-part moulds consisting of a base and two sides. This is good news because, should I want to make my own mould, I would have a flying start at using the bases of the existing ones to do it (and making my life a lot easier). More rubber bands and a luggage strap were involved.

I proceeded to fill the moulds using a plastic jug until they were full to the brim. I did this one after the other so that a little production line was established. The slip would sit in the mould for 15-17 minutes before being up-ended on the barrel for the remaining slip to pour out for 15 minutes as the next one was filled and so on.

Here’s the cunning part: they can dry out overnight so that (fingers crossed I don’t destroy them on the way into the studio) I can work on them in the morning straight away! Woo hoo. No praying and rain dancing and whatever else I end up doing while waiting for the stuff to dry out of the moulds.

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Pretty excited to see how they come out. This is a medium I really think I could develop, but I am afeared that my general clumsiness will mean I somehow put a foot through it during the day.

The other part of the plan for tomorrow is to make some sample tiles for the glazes and get those bisque fired and ready to go.


So, I have now made two batches of these bad boys. The first teapot came out a little on the thin side at 17 minutes, so I left the second for 20 minutes and it seems perfect, not too thick, not too thin.

I cut off the spare and buffed the “seams” with a needle and a wet sponge, before leaving them to dry. I used a bit of the spare to make a test tile to see whether the slip will survive the two firing temperatures. Good news: it came out of the bisque firing unscathed (1000 degrees), but I suspect its the glaze firing that will be the true test!

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The test tiles for the glazes (pure stoneware so no risk) are still awaiting their glaze firing.


The test tile survived! Hurrah! It is a darker brown than I was expecting and with lots of flecks indicating a high iron content to the clay.

For the first batch, I used a simple set of dip glazes available to all at the studio: a matte black which comes up a lovely reddish rust colour, and an oil-slick black which is hyper shiny and pure black.

First you mix the glazes as they tend to have a lot of sediment at the bottom, making the liquid part very thin. This can be a greater (45 minutes) or lesser (5 minutes) job, depending on the glaze and how long since it was last used. You dip the lighter colour first (to avoid cross-pollinating the batches) by simply lowering the bisqued pot into the glaze for 5 seconds and removing it, rotating it gently in the air above the batch to avoid drip marks.

You wait for it to dry (worth some patience here) to the point where you can pick it up without leaving smudges in the glaze/fingerprints, rotate it and then dip the darker colour. I also poured a jugs worth in so that it glazed the inside and the spout. You wait for it to dry again and can then use the bottom washer (like a belt sander except with wet carpet) to remove the glaze from the bottom so that when it is fired it doesn’t melt and stick your work to the kiln shelf.

Only one mug has been glazed so far because the oil slick is so pervasive it pollutes everything it touches and I haven’t managed a clean second dip so far! I was in a hurry and washed the streaky glaze off and tried to re-glaze straight away but that just left me with lines where the glaze had diluted too far. I also hadn’t remixed the glaze so it was far too thin. Oh well, sixth time the charm…


 

The results were very pleasing apart from a tragic finger print on the rim of the lid.

And so mass-production ensues:

The next step was to try out the Duncan glazes. I applied them liberally (perhaps too liberally) with a brush with a satin white glaze on the interior. They look very vibrant when applied: quite like poster paint. As they dried the brush strokes appeared to vanish.

Once fired at 1260 degrees C, the change was remarkable. While the glazes lacked the lustre and the vibrancy of the test tiles, the clay showed through pleasingly making for a much more muted and subtle effect. The brush strokes were also very much in evidence:

Anyway, let me know what you think! I will be putting further experiments with this shape under a separate post. And I realise I have left out the test tiles, which I will remedy shortly!

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