Birthday Glaze

20180209_161019 (600x800).jpgRenata held a fun glaze workshop with us in which we made a glaze based on our date of birth. We randomly chose glaze materials to mix in proportion to the year, month and day we were born. By comparing each other’s glazes we could get a good idea of how each material behaves when fired.

My glaze was the result of mixing a high proportion of whiting with some dolomite and ball clay and a small amount of Wood ash. Fired to stoneware temperature the result is a very dry, matte  and slightly flaky off -white/pale green glaze blending into pink lower down in a gradient effect. The ash has pooled in a shiny green line along the base where it has melted. It’s not suitable for functional ware because it hasn’t fully melted, but I’m excited to use it to decorate sculptural forms.

Whiting (calcium carbonate) acts as a flux and also creates matte effects (as does dolomite). Ball clay is a source of alumina and enhances glaze suspension. I want to make a series of glaze tests using the same four ingredients but changing their percentages so that I can get a better glaze fit.

 

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Field: Development into 3D

In my tutorial with David last week we discussed colour theory and the way putting colour on the back of flat planes can reflect the light in a halo of that colour around the edges. As an example he suggested I look at the first year fine art project displayed on the third floor – I hadn’t looked closely enough at these to notice the optical effect before but it makes the images pop. I glued some coloured paper to the back of my cardboard cutouts and the result above shows a very subtle halo of green and red light shining behind them. It reminds me of the hazy reflection of light you get on overcast days like the ones we had at Port Eynon. If I manage to make some of these in porcelain paper clay I could glaze the backs to get a similar effect.

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After Laura’s plaster casting workshop I was keen to try printing onto plaster because I hadn’t tried it before and I saw the opportunity to make more slab-like forms which I could assemble as a kind of theatrical scenery. I rolled coils of clay and pressed these onto an inked up plate, creating walls around different sections. Next I poured in plaster to a thickness of about 1cm and reinforced the back with scrim. I mixed up two lots of 2 pints water/plaster so I didn’t have to do the whole plate at once. I should have been much neater with the clay by cutting walls from a slab because I would have had to file down the edges less this way. The resulting sections are a bit too thick – maybe I could have poured the plaster sooner. On the plus side, lots of detail came out from the intaglio plate.
I then set these upright in a bed if plaster (4 pints) which again, was poured a bit late so looks like icing slapped onto a cake with a palette knife. The scene looks a bit naff and reminds me more of a snowscene with ice and glaciers than a beach. I like the idea of placing a second inked up plate onto the drying plaster then hanging up the sections when they’re dry so the print is shown on both sides.

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I also tried using coloured slips and sgarffito on slabs of clay. Inspired by Morgan’s Vicarious Wednesday talk I tried using paper resist stencils but discovered I have very little patience when it comes to decorating. Hopefully the slabs below will fire black and white.

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Slips brushed on White St.T

I’ve also been working on making paperclay for the first time. Porcelain casting slip can’t be used for this purpose so instead I had to use porcelain from a bag. I dried out the clay then ground it to a powder in a pestle and mortar, added water, then let it slake down overnight. In the morning I poured off excess water and soaked the paper pulp (ratio of 1:3 to the clay) for 2 hours before sieving it (60 mesh) to get rid of excess water. I mixed the paper and slip together by hand but the consistency was very lumpy so Matt showed me how to use the glaze mixer which blends the paper pulp into a smooth consistency.

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Sieving the slaked down porcelain before adding paper pulp
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Glaze mixer

I made up an ink with black underglaze, a small amount of borax frit to make it less powdery (about 5% is ideal) and copperplate oil. The powders were sieved through 200 mesh then the oil was added gradually, applied to the plate and rubbed off with scrim the same as with the intaglio ink. This afternoon I built a wall around the plate and poured in the porcelain paperclay slip with the hope it will be dry by tomorrow with the ink printed on. The underglaze should stay on when fired but it will need a transparent glaze to seal it. I’m worried the clay might not dry in time for tomorrow’s assessment so I may try using a heatgun to speed up the process.

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Inking up the plate

Katharine Pleydell-Bouverie

Dwi di ddewis ysgrifennu post yn y Gymraeg am y tro cyntaf ers i mi gychwyn yn y brifysgol dros flwyddyn yn ôl, i weld sut mae’n teimlo i newid iaith wrth siarad am fy ngwaith.
Des i ar draws casgliad o waith cerameg Katharine Pleydell-Bouverie yn yr amgueddfa ‘Potteries’ yn Stoke, a syrthio mewn cariad hefo’i gwydreddau lludw. Roedd y gwydreddau mewn arlliwiau o las, gwyrdd a llwyd yn dibynnu ar ba fath o bren oedd wedi cael ei losgi. Yn y llyfrgell ffindiais ei rysait gwydredd lludw a chymysgais hwn hefo’r lludw oedd ar gael yn adran cerameg CSAD (dwi angen gofyn o ba goeden daeth hwn) Isod mae’r gwydredd sydd wedi cael ei danio i 1280C mewn gostyngiad.
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Rysait gwydredd afloyw syml KPB:

Lludw                          40
Feldspar potash        40
China clay                  10
Ball clay                      10
(Mae ychwanegiad o 10 gwarts yn gwneud o’n llai afloyw)

Y canlyniad ydi gwydredd gwyrdd gwelw, naturiol. Fy mwriad yw casglu lludw o gyfres o brennau gwahanol a gweld sut mae’r lliw yn newid hefo bob un. Gallaf hefyd newid y feldspar i roi effaith gwahanol (mae’r post diwethaf yn profi hyn). Dwi ddim yn sicr sut i gasglu’r prennau, gallaf brynu nhw ar-lein ond bydd y prosiect yn fwy personol os gallaf gasglu’r pren fy hun.

Dwi’n gobeithio defnyddio’r gwydreddau yma i addurno’r gyfres o jygiau dwi wedi taflu mewn clai white st Thomas. Gobeithiaf dysgu mwy am danio gostyngiad oherwydd bod y lliwiau yn fwy soffistigedig ac mae’r clai yn troi’n lliw hardd mewn awyrgylch isel mewn ocsigen. Dwi di ddod o hyd i lyfr ‘Katharine Pleydell-Bouverie: a Potter’s Life 1895-1985’ yn y llyfrgell sy’n cynnwys lluniau a ryseitiau gwydreddau wedi gwneud hefo lludw cedrwydd, cnau Ffrengig, drain, rhosyn a.y.b.. i grochenwaith caled. Er bod ei gwaith hi wedi cael ei danio hefo coed tan, dwi’n gobeithio cael effeithiau tebyg hefo tanio odyn nwy.

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Matt Glazes Cone 10.R

Thinking about the surface effects I’ve identified I liked in the past I found a Mamo Matt glaze in Jeremy Jernegan’s Dry Glazes handbook and made the following variations:

Original: MC36 (W1)
Potash feldspar                     50
Dolomite                                 20
Whiting                                   4
Calcined china clay              21
Tin oxide                                 5

W2 – Replaced feldspar with 50 Soda feldspar
W3 – Replaced feldspar with 50 Nepheline Syenite
B1 – Original recipe with 1% cobalt, 8% black iron and 3% manganese
B2 – Original recipe with 4% black glaze stain

Fired in Reduction to 1280C. It was surprising to see how just changing the feldspars could change the colour so much. The potash gives a brighter, more clinical white than soda while the nepheline syenite gives blushes of pink and orange. The manganese gives a matter, more metallic black than the stain which gave more of a dark green undertone. I like the manganese black glaze (below) a lot because of the oily way it reflects the light without being too shiny. Application is better when poured.

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Below is the piece I worked on over the weekend, throwing in sections with white st Thomas then joining them together on the wheel when leather hard. Already you can see a wide ranges of tones of light and shadow and a series of ellipses when looking through the form. I enjoyed the process of making this piece and the way the pieces slotted together like a jigsaw puzzle.  The next step is to make more of these composite forms but trying to make them less symmetrical and on a smaller scale (maquette size).

 

 

And now for some bowls

 

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For some reason I find throwing and turning bowls more difficult than other forms. I can never seem to get the thick clay out of the base and they tend to end up with strange ridges. The pearlescent glaze here was supposed to be a gloss white but looks like it needed more than one layer.

Page 132 The Glaze Book – Gloss white 1290C

Potash feldspar                              60
Dolomite                                         20
Quartz  (flint)                                 15
China clay                                       5
Rutile                                                5

Layered on top of another glaze the opalescent effect might work but I don’t like how watered down it looks revealing the clay underneath here.

The bowl with the oatmeal glaze is my favourite – it’s got rings of different shades of orange with a subtle texture and green tinging where it’s pooled at the base. I like the detail of the running green glaze around the rim too – a touch of Lucie Rie!

Oatmeal 1290C

Potash feldspar                             45
Dolomite                                         88
Quartz    (flint)                               16
Zirconium silicate                         11
China clay                                        6
Zinc oxide                                        2
Chrome oxide                                 1

The green bowl has a pleasant mottled antique green colour – white slip with smooth satin opaque yellow green on top applied to bisque ware. I like the visible brush marks and the colour variation where the thickness is different.

Natural glazes

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I’ve been invited to sell my work in my local hometown and want the glazes to reflect the colours of the rural landscape of North Wales. These thrown vessels have been painted with the glazes I made at the start of the year as part of the local clay project. The bowl has been pained with a glaze made from a 2:3 ratio of Potash feldspar to my clay while the rounded pot has a 2:1 mixture of Whiting and my clay. It flows very much like an ash glaze but luckily wasn’t too runny that it stuck to the kiln shelf. I’m going to add more whiting and feldspar to these glazes because the colours are much darker than I expected.