Tag: casting

Disasters in casting

Design, Sculpture

10 am – My latest attempt made last night, was looking very good until

I tried to remove it from the mould –  it broke . . .

third failed casting

I have learned at least three things from it though – mix up one large batch not 2 smaller ones, add a retardent so that I have more  control, remove it from the mould more carefully.

Fourth attempt coming soon.

3pm Tuesday – I have made another casting pouring the whole thing at once, instead of in two layers. I could not get the surface to be smooth whilst the plaster was wet and have done a lot of scraping back with various scrapers. Its not as smooth and even as I’d like but its OK. I must now be patient and not try to take it out of the mould/wok until tomorrow. Then I hope to be able to fix the small imperfections., remove it from the mould and make the second half.

fourth casting

32 hrs later  8pm GMT – the casting is out of its mould and in one piece! although the scauce-pan lid is firmly stuck in the centre. Experience suggests I leave it well alone, the whole thing kind of slid out of the mould at lunchtime today 1pm GMT – with a little coaxing but the lid is stubborn and has decided to stay where it is a little longer. The outer surface is looking good albeit somewhat stained with rust and felt-tip pen. I think I will sand that off in the morning. Showing here, the stained exterior and the still-lodged saucepan lid.

Fourth casting de-moulded - looking good

Several days later (Friday) the casting is hard and almost dry, I managed to succesfully  remove the saucepan lid but later on several fine cracks appeared and its is in danger of breaking apart. The very kind man at Maragon casting suppliers, suggested that the cracks are almost certainly caused by my having added a wee few drops of citric acid to the mix to slow down the setting period when I needed extra time to smooth the interior surface. He suggests adding a fresh layer without the acid, to the inside to strengthen the structure.

I might just start again as the rust marks, also caused in some part by the citric acid but mostly caused by the long time it takes to set, are almost impossible to remove entirely. (I will heat the next one very gently in the fan oven, to speed up the elimination of the water content and reduce or even prevent rust forming.)

Cracks in the drying casting

Experiments in casting

Design, Sculpture

Hopefully I have learned enough from the last two experiments to make a good casting this time.

I set up the wok again with Plasticine walls and a slightly larger saucepan lid and made up a much larger batch of plaster hoping to cast the whole thing in one go.

I poured the plaster into the wok and started swirling it genlty, hoping to make it stick to each part of the surface – impeded somewhat by the thick layer of petroleum jelly. During the next 10 minutes the plaster gradually thickened and began to build a smooth layer over the whole surface area. As I swirled the liquid it behaved like a tidal wave coming around and around in a regular sweep but as it began to set it grew thicker and was in danger of leaving a literal tide mark in an unsuitable way. I set the wok down to rest and watched as the excess plaster solidified in an almost even spare-tyre kind of shape  in the centre.

I decided this time not to try to manipulate the surface in any way and I am pleased to say that it is smooth and even, though somewhat thicker towards the centre with a discernable swelling about 2 cms from the pan lid,  it looks pink here but it dries white.

second casting

I suspect that the outer/upper edges are fairly thin and that I will need to make another pouring.

Experiments in casting

Design, Sculpture

I wanted to make a “stone” version of a form I have made often as jewellery, the Reuleaux Triangle – the original form developed by the mechanical engineer Franz Reuleaux  in the late 19th century.

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  • I needed to mark out my new wok – I couldn’t  find a set of dividers large enough – 25cms, so I made a very simple one from strips of wood. I borrowed a wing nut, bolt and nut from something else, cut two pices of 30cms and one 18cm long, drilled some holes at roughly .5cm intervals on the short piece and used two nails to fit them together, added some points just with sellotape.
  • I marked the wok roughly in blue felt-tip pen and then found the centre-point using the dividers, drew a circle, divided that into six. I drilled a small indent at three of those points and used those as the centres to draw the three arcs.
  • I made Plasticene walls along the scored lines and set a  saucepan lid at the centre to form the central hole. I hoped that brushing the whole thing with petroleum jelly would make it easy to remove when set.
  • Using Cassini’s plaster from Maragon,  I mixed up a test bacth that was enough  to coat only about half  of the mould, I added progressively both by making more mixture but also by scraping the surfcae and using that to infill gaps. Not a good idea as it turned out.
  • The plaster becomes very hard and waterproof after maximum of 5 days but is workable to varying degrees for 2-3 days, at 15 minutes it seemed a bit like cheese, almost rubbery and not easily spread out or carved, though i did try to scrape the surface smnooth with a swan-necked cabinet scraper and what is charmingly called an Alabaster Knife from Tiranti, sculpture suppliers in London
  • 24 hours later it was dry enough to slip clear of the wok, petroleum jelly works but the uneven inside surface was terribly difficult to work on, dimpled, rough and flawed and the outer surface was marked with poorly patched areas, badly mixed plaster (small inclusions of plaster dust), rust and ink stains as well as bubbles!
  • So – it had to go in the bin . . .

 

 

 

 

 

 

Experiments in casting

Design, Sculpture

I have never tried casting anything in plaster until now, using the large nylon salad bowl my mother gave me 20 years ago as my modelling form.
Playdough walls to define the shape and everything covered liberally with Vaseline. I poured the plaster and allowed it to thicken and spooned out the excess. I made two castings and after finishing them to a smooth polished surface, I glued them together.

Geometric Sculpture - Relueaux Triangle on a copper rotating base
As I failed to realise how fragile it was, ordinary Plaster of Paris without an armature, it broke . . .
Now I am starting again but bigger and better. I have acquired a large wok and a bag of terracotta coloured sculpture plaster which not only is very tough but also has iron inclusions which will gradually rust on the surface.