Slip and pinholes…..

Photo 19-04-2013 10 32 00Been a bit busy at work recently, so not had much time to crack on with this, but whist the ball is in the kiln being fired I made up some new slip to cast some more balls. Slip is basically liquid clay, clay particles suspended in water. I could buy it from ceramic suppliers, but I thought I’d mix up my own (keep the home made feel to everything)

I started with some clay that had been soaking in water for a while, making it all squishy (a technical term 😉 ) then just got stuck in with my hands squidging and squeezing (again, all technical terms) it through my fingers to mix it into a thickish slurry – you can use a drill with a mixer attachment for this as well, and I probably will when I make up a larger batch – you’re looking for it to be faily thick but not too thick, something like the consistency of cream. It then needs to be sieved through a fine sieve to remove any big lumps and make the slip smooth. A deflocculant is added to keep the clay particles suspended in the water, in other words, it stops all the clay settling to the bottom of the container. I used some sodium silicate for this, dissolved in a little bit of warm water. The slip was then poured into the storage container.


Mixing up more slip

The next day the ceramic ball had been fired, it looked good, felt a nice size to hold and appeared to be light tight – I was worried that the walls might be too thin that a bit of light would sneak through, but it looks fine. It’s still a bit rough looking – I’ll have to work on that on the next ones.

fired ball 2 up

first fired ball

Ok – time to make the pinhole for it. For any photographers following, you’ll all probably be familiar with how to make a pinhole, for those who don’t, here’s how I make mine…

First I worked out what’s the best size to make the pinhole- this depends on the focal length of the camera (the distance from the pinhole to where the film plane is) – in this case the distance from the hole in the ball where the pinhole plate will be and the back of the ball – it worked out at around 11cm. There’s plenty of websites out there that will calculate optimum pinhole sizes based on focal length, and vice versa, I tend to use MrPinhole, Mr Pinhole told me the best size for my pinhole is 0.45mm.

I gathered the bits I needed: a bit of thin tin, a 0.4mm drill bit and Archimedean drill, a bit of blue tack, a ballpoint pen, fine wet and dry paper.

Start off by placing the tin onto the bluetack, and press the ballpoint pen tip into the tin to make a small indentation (I forgot to photograph this bit), turn the tin over and sand down the bump made by the pen tip – this makes the tin even thinner for when you make the pinhole. Turn the tin back over and drill the pinhole where you made the dint, use the bluetack underneath to stop from drilling holes into your table top (if you do accidentally drill into the table top, drill loads more holes and blame it on woodworm). Flip the tin over again and sand down the back of the hole to make it smooth. This also enlarges the hole slightly, so my 0.4mm hole should go up to around 0.45mm – what I’m looking for.

As the surface of the ball is round I curved the tin pinhole plate slightly so it would sit better on the ball. I attached the pinhole plate to some heavy duty tape (with a small square cut out to allow access to the pinhole) and coloured the exposed tin black with a Sharpie, just to cut down on any stray light bouncing around the inside of the camera. The tape will allow me to stick the pinhole to the camera.


making of the pinhole

So the pinhole is now ready to attach to the ceramic camera – I just need to make it light sensitive, that’s a job for next week ……


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