Technical project…  … 80 shades of blue…

Having an interest in slip-casting as part of my professional practice I decided early on that my “Technical exploration” would involve the testing out of coloured slips. This pigmented medium would be of a colour which would be used next term in my final works. My aim for this project would be to create a series of tests which could be cast as one individual piece and displayed on a single fired artefact. It was at this point that I looked back to my mould-making skills and decided to create a large flat mould in which I could pour all the different shades of my chosen colour slips, (in the form of a sort of giant ice-cube tray). Further to this by pouring stainless clay slip body over the top I would create a single piece of work which then incorporated all my individual tests.

I have worked with clay pigments and oxides and stains in particular extensively previously, I was well aware of the broad spectrum of shades which could be obtained by slowly increasing my addition of this powdered substance to my liquid clay body. I therefore decided to embark upon a large scale project but narrowed my testing down to one colour.

The colour which I decided to test was a shade named “Peacock Blue” which is a high fired ceramic stain obtained from “Bath Potters Supplies”. Having gained prior knowledge of mixing stains with liquid bodies and being in possession of a process driven attitude helped me greatly in this task.

I decided that I would test this pigment in small variations of addition, taking 100g of liquid clay slip body I would add the stain in increments of 0.25g until I arrived at 20g of product. These small additions of this beautiful colour would I hoped give me a wonderful range of shades and an exciting palette of colour from which to work on future projects. In all I would have to mix eighty tests individually, carefully and with the greatest diligence, any discrepancy could see the whole project ruined and days of work for nothing.

I had now the information I needed to create my mould. This mould I decided I would initially make a form in soft modelling clay which I would then make a plaster cast of thus making my mould. I rolled out two large slabs, one I cut to the desired size the other using a pastry cutter I cut out the small tiles which would eventually show as depressions in my mould once finished, the shape I used for this was a small hexagon. Measuring my slab I worked out how I would fit my eighty little hexagons onto my template so that they would fit evenly into eight rows of ten, thus creating a large rectangle.


Once the “Former” was complete I wheeled it down to the plaster room on a trolley where I “cottled” it up and mixed and poured my plaster. I decided to use “Prestia” mould making plaster for this particular mould as it is a more durable and more importantly a denser plaster than the standard mould making variety used at the university. This added density I hoped would increase the life of the mould but more importantly decrease its absorbency which would give me more time to work on the castings without them drying out too quickly.

The mould complete I left it in a dry place so that it could dry, I did not want it to dry out too much however as then it wouldn’t allow me the time I needed to complete the casting. I at this point arrived at my next question, which clay slip body would I use? Predominantly casting in Fine Bone China slip I initially thought of using this, however on my first attempt it was obvious to me that a mould of this size was going to cause me real problems casting in this unforgiving material. The first piece as one can see tore when leaving the mould.

I had for some time been testing out another product called “Parian”. Parian slip is named after “Paros” the Aegean Island which is world famous for its white marble. The clay body contains a very white feldspar which enables this clay to fire a brilliant white and is beautifully translucent when thinly worked. It is also a self-glazing material, which means it is a more economic material to use as it only requires a single firing. I decided that this would be the material for my testing as it is both more forgiving than Bone China in its handling and being self-glazing.

Having measured out eighty pots of 100g of Parian Clay Slip Body I started the task of adding the “Peacock Blue” Stain to these pots in increments of 0.25g, for which I used a goldsmiths scales in order for the measurements to be precise. I videoed this process.

Once this lengthy task was completed I set about mixing each individual pot and sifted it twice through a plastic 100 mesh test sieve. It was at this point I could start to see the range in shade of pigment which I was looking for, it was for me very exciting. The scale of this project was massive, mixing the pots and sifting alone took me 800 mins 13.33 hours! I videoed this process.

Once the mixing was completed I decided to move the pots and line them up in the corridor, photograph and video them in order to see the scale of the project so far. I must say I really enjoyed filming this part and watching, mesmerised by the movement through the increasing or decreasing shades of the colour by increment, so interesting and something I must revisit at some future stage.

I then organised my pots and space for the casting of the colours and the tile itself. This was the tricky part as if the mould was too dry the casting would dry out too quickly and therefore become stressed and uneven, if it was too wet, well, it was likely to stay in the mould. I decided upon looking at the mould that it was too dry so pours a few litres of water into it to slow down the absorption rate. I then made another video of the process of pouring the mould.

When the mould was turned out it was clear to me that I had been right to add water to the mould as some of the coloured tests had shrunk whilst I was completing the task and the slip of the main body of the tile had found its way under and around some of the tests. This was rectified by extensive cleaning individually test by test!

Having completed this task my tile now lies ready for firing.


Top Left 100g Parian + 0.25g Stain… … Bottom Right 100g Parian + 20g Stain.

When cleaning the tile one can see that the blue stain dust created has in parts literally stained the background body of the tile, I have therefore decided to bisque fire the tile to start with and then sand the tile back to the preferred whiteness.

While it was firing I decided to create another series of individual tests using my mould. These also where very successful.


1=100g Parian + 0.25g stain, 2=100g Parian + 0.50g stain… …80=100g Parian +20g stain.

The concluding evidence of this technical project is unfortunately not yet complete, although in its raw bone dry state still one can see quite clearly the result of the task. In its unfired state it is easy to see that at lower additions of pigment the movement in variation of colour is far quicker this  slows considerably when arriving at around 5% but continues to be visible throughout the tests.

I will add more content to this archive when the tile has been fired along with more photographs and technical information regarding the firing itself and outcomes of the firing.

I have been on a wonderful journey through the movement of shades of colour by minute increment, which I have, I hope, well documented and thoroughly enjoyed.

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