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Old 12-15-2016, 09:47 AM
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Pete VanderLaan Pete VanderLaan is offline
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cork and molds

Michael Ahlefeldt-Laurvig

Ive tried linseed oil and never got it to work well for me- now I know why.
Here is an alternative which is less labor intensive- it does involve using traditional or old style boat varnish, lacquer or whatever you like to call it and thats a bit of an issue because Ive found some that works but Ive also tried other brands that call itself the same thing and it does not work. (makes small scratches on the glass) Its a rather thick slightly amber colored varnish that hardens to a hard shiny surface.
Its all the same process for cast iron or graphite, large or small, same temperature and timing.
Sounds like my cork is a finer mesh than Ed s- wild guess is about a 200 grit if I compare it to sand- it is very dusty and light. I keep it in a plastic trash barrel with a tight lid- don't want any contaminants in there- sand dust etc.
If its a new mold I clean it with acetone. Its good if the mold is warm ...100 F- paint the inside of the mold as even as possible liberally with the varnish- work fast and don't let it sit- the varnish will run. I immerse the whole mold in the cork, not pushing or packing it against the varnished surface, just covering it and let it sit for 20 minutes. Take it and tap the mold to get the excess off but don't touch the cork surface even if there are clumps of cork. Run it for 6 hours in the annealer at 410 F (210 C)
If you screw up programming the controller or choose the wrong program and it goes to 950 F you've ruined a graphite mold- it looks good but becomes porous and gets water logged when you dip it and crackles the glass when you blow in it- I don't know of any way to save it, and you have to get a new mold…
Take the mold and brush off any loose cork with your fingers, then blow a thicker than normal gather into it to burn the cork (no water)- stay in there until it quits smoking. Clear the holes from the inside of the mold with a nail or wire then repeat the whole process one more time.
Now check the holes - there is a tendency for cork to build a little ring around the holes so you can take a sand paper and take down any ridges- I use used belt sander paper- no grit comes off. The mold is ready to go- no breaking in- and will also do about a 1000 stemware cups before redoing it- but then its enough with one coat of cork.
I don't leave my molds in water overnight, but if its not been used for a couple of months it might be an idea to soak it 12 hours before use.

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from: http://talk.craftweb.com/showthread....=corking+molds

There is such a thing as paste free- or freely translated from swedish- self lubricating graphite, but its only been around a short time, 30 years or so
That could be the type Ed was using.
Ive had molds made in it a couple of times but have always finally corked them anyway to get a better surface result. Corked molds are more forgiving.
I have a feeling they work better in a serious production setting where you can really control mold/glass temp and timing. I have a barn full (well, hundreds) of old graphite molds from the 1960s and they are all pasted and vented with holes. They used carbon powder and linseed oil instead of cork back then. Sometimes the coating is a couple of mm thick.
By the look on the prices on eBay of those molds I have a substantial fortune laying around- They will become the worlds most expensive land fill material one of these days
Jacqueline is right about the non turn forms not being pasted and I googled pilgram glass and it looks like they have made a lot of “crackled” glass- dipped in water- and that would tear the hell out of a wood or corked g. mold.
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