To make a mould ...

[Nevthedigger]

Hi, newbie here with a request for advice. I am fairly new to glassworking in the kiln, but am keen to try out some ideas. I need somebody to advise me: What I am trying to do is take an impression of an antique bottle and cast a piece of glass to pick up the embossing. If you can understand what I intend to do, I wish to use a pad of clay of some kind, roll out the embossed bottle like a rolling pin, and then lay a piece of glass over the impression to cast. Question - what sort of clay would I use / is there a special product available to do this?

[Flyingcheesetoastie]

Hi,

Are you intending to use flat glass to make the final impression or actually cast the glass into a mould?  Either way you probably won't be able to use just clay and glass as the glass would stick to the clay.

What I would suggest is to make a refractory (plaster based) mould to slump the glass onto.  To do this you would make the impression in the clay, this will be glass once finished.  Then you need to pour a mould over the clay, i use a 50/50 mix of plaster and flint but you can also buy other mold making mixes from suppliers.  Once the mold is set you remove the clay and clean any excess away.  Allow the mould to dry as much as you can before firing and you will also need to add a mold drying stage to the firing, something like a ramp of 100 degrees per hour up to 500 degrees then a 1-2hour soak.  This takes out all the water from the mold without damaging it or the glass on top.  The kiln should also be vented during this process to protect your kiln from moisture damage.  The rest of the firing will depend on the glass you use, the thickness etc.

I hope this starts to answer your question and please feel free to ask any other bits and pieces.

Rachel x

[Nevthedigger]

That's a fine comprehensive answer, many thanks. I half guessed that a pad of clay on its own would cause problems. Food for thought, I will be experimenting when I have acquired the necessary materials .... I did have limited success by sieving a layer of powdered batt wash a few mm thick and then rolling the bottle over it, but it was a nightmare to do without "smudging" the impression, and took a few attempts to get an acceptable 'mould'. Any good and reasonably priced UK suppliers to recommend for the flint and plaster (or do I use ordinary DIY plaster?)

[Moreton]

Hi Nev & welcome. I can recommend Potclays in Stoke on Trent. They carry full stock of everything you would need, Potters Plaster, Silica Sand, Flint etc etc and so many clays that you are spoilt for choice. They do deliver but can be pricey due to weight of those types of material but a visit would be well worth while if you could. Lots of free advice an d very friendly people. Occasionaly they have sales with good discounts and there are always a few bargains on offer for visitors. http://www.potclays.co.uk. Best wishes and good luck. Pete

p.s. register with them for special offers

[Flyingcheesetoastie]

You need fine casting plaster, not DIY stuff.  The flint it the more expensive of the two and I'd recommend seeing if there's a pottery supplier locally who can either deliver or you can pick up from.  Ask around, there's bound to be one, although if you're not doing many moulds then just get half a kiln of each to start off with.

[Warm Glass UK]

We have a range of casting materials and there's a good tip sheet from Bullseye Glass that you can downlaod here : http://www.warm-glass.co.uk/Downloads/Public/Products/Casting/TipSheet_05.pdf

Pippa