"Cleaning residual rubber off bronze or brass masters" Topic

So Ive just pulled a load of small metal masters out of a vulcanised mould (J cokers Grade60 disc – Im in the UK) and they are BLACK. Absolutely coated with rubber in all the fine details – does anyone have any tips or tricks for cleaning all the rubber off them? I have a feeling Im going to need to mould them again.

I completely give up with the grade60, I dont know if I should be leaving it for longer before I crack the mould open or what, but I never have the problems I have with the J100 discs Coker do?

Really hoping these brass masters arent ruined, dont want to have to wait weeks for shapeways again.

Thanks.

Check the temp of the plates on the vulcanizer. Are both getting hot enough? Is the pressure gauge on the press seem correct? Sounds like either you took the mold out before it was totally cured (generally, one hour at least….longer will not harm the mold, but too soon and you will have a mess).Did you dust both sides of the mold before placing in the masters and lock nuts?…OR you received a bad batch of mold rubber!

Check with mold rubber maker to see what they recommend to clean the rubber off the mold with (solvent type that will dissolve the material from the brass). Yes, you will have to remake the mold as anywhere there is rubber on your master will be a filled in void on any castings made subsequently.

Good luck, RF.

v/r
Tom Dye

Yep, dusted both sides, the whole mould was cured but too much came away in the small details – perhaps the Grade60 needed to be left in a lot longer than the hour-and-three-quarters I leave the J100 in… Like I say my mould making goes perfectly every time when I use J100, I ordered a few grade 60 hearing they would be better for small flat pieces, but every time I've used them they've just been cr*p. :(

I know of no solvent that just dissolves rubber – I will try acetone as I have it to hand and it dissolves everything else. Otherwise Ive just ruined a customers £200.00 GBP brass.

Some grades of brass, nickel etc do react with rubber during vulanising so I've heard. In the jewelry trade they often plated such like before moulding them. Not been there but lighter fuel ( essentially petrol) with a tooth brush might work as is disolves rubber but try it on something that deosnt matter first in case it makes things worse. I get a discolouration on some of the brass Ive used but never chunks of rubber sticking to it.
Use the 50 grade and silocone myself as find the 60 too hard.
Otherwise as Tom Dye suggests contact Coker and see what suggestions they have.
And I do know how you feel a bit lost a bunch of Masters many years back when a seal on vulcaniser failed…………
doubly worse when your handling someone elses Masters.
L

The copper in the brass probably reacted with the sulfur or something else in the rubber.
Any brass, copper or bronze (yellow metals) masters should be coated with a special model coat before vulcanizing. It is a purple solution that is brushed all over the models and dries in a matter of minutes. It's widely used in the jewelry trade.
I bought an 8 oz bottle many years ago and it's still good. It was sold by Contenti in Rhode Island and is called Contenti Model Coat No. 210-504.
I don't know what it is made of as no contents are listed on the bottle. Check good jewelry supply houses and ask questions if you're not in the USA. I do know it works.
Try spinning your mold to see what you get, but you'll probably need to make a new mold after cleaning the gummed up masters with solvent or lacquer thinner.
Toby Barrett
Thoroughbred Figures