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Topic: Working with latex
Message: Posted by: Starrpower (Oct 21, 2005 02:43PM)
Does anyone out there work with latex molds? I have a few books on the subject, and have found that a material similar (or identical) to dental moulage is used for forming molds. But I'm interested in making collapsible bottles (hollow, 3-dimensional.) Any experience out there or sources of information? I've been able to duplicate the color and consistancy I want, but I can't seem to create a workable mold! I've tried plaster with exremely poor results (not smooth, leaves a residue.)
Message: Posted by: kaytracy (Oct 21, 2005 10:34PM)
YOu do not say what material you are making the castings out of, foams? if so consider a latex skin inside the mold- we do very detailed masks this way. pourable latex into the mold- wait 30 seconds, then pour out, allow to skin up, then foam it.
We use plaster molds with great sucess for what we do. just be sure it is good quality and clean. Use a good shaker table, or a plug in vibrating device (<blush>) to remove the bubbles, unless you have a vacuum jar to pull them with! it makes for a very smooth surface with next to no defects. Inspect the molds before use, and fill in any holes from bubbles first!
Also-be sure to use a good quality mold release on the plaster (I do my hand grenades for re-enactment work with plastermolds also)
Message: Posted by: Starrpower (Oct 22, 2005 10:35AM)
I'm using liquid latex with colorant and hardeners added. I'm trying to make the collapsable Nielsen-type bottles. It would be far easier and cheaper to buy 'em, but he doesn't make what I want. So, it's not a solid-foam bottle, but a hollow, latex-skin bottle.

It's the mold I don't know how to make.

How you you make a 3-D mold? Two parts? What kind of plaster? My paster molds have tons of air holes, and leave all kinds of powder residue behind. I've been using plaster of Paris. I am using a mold release.

I have no idea what a shaker table or a vacuum jar is. I know what a vibrating device is, but I doubt it's the same thing you're referring to! Would it be necessary to have some sort of rotational machine, or will simply rotating it by hand until the inside of the mold is covered suffice?
Message: Posted by: Leland Stone (Oct 22, 2005 11:00AM)
Kaytracy's got good advice, to which I'll just add a link I've found handy:

http://www.smooth-on.com/default.htm

Good luck!
Leland
Message: Posted by: mvmagic (Oct 23, 2005 04:02AM)
For plaster molds you should use dental stone (like die-stone or die-keen), which is a really tough plaster. Extremely good plaster is also Ultracal 30, which is propably the most used plaster in make-p FX industry. The best mold (lets not talk about silicones and such, they're a bit complex) you can do with Epoxical 415 (as the first surface) backed up with Ultracal.

A shaker table is used to get rid of the air in the plaster. You place a mixed vat of plaster on that and it shakes the air out. Vibrating device you place in the plaster (looks a bit like mixer) and it does the same thing.

If your plaster has lotsa airholes, I think you're mixing wrong and propably using too thick mix. To begin with, always add plaster to water, never water to plaster. After adding the plaster to water, let it soak for a few minutes before doing any mixing. After the soaking, start mixing with a wooden spatula or the like, being very careful not to mix in air. You can shake the vat yourself as well to take some of the air out.

A good way to reduce the amount of air is to use more water than usual so the plaster mix is kinda runny. It takes more time to cure but the end results are good-a very good surface with an almost ceramic look to it. Still, if you increase the amount of water in the mix, the right mixing is still important in order to prevent the airbubbles from forming.

The molds...well, if you have no previous experience in mold making a single piece mold would suit you best so you can just slush-cast your piece. Much depends on your master-if it has deep undercuts and such a two-piece mold might be neccessary, however they are a bit complex to do well if you have no experience.

Just remember that latex detoriorates over time-it gets stiff and yellow. You could also try using balloon rubber as a bit thicker cast to see whether it works ok.

If you have questions, PM me, I work with molds a lot.
Message: Posted by: makeupguy (Nov 27, 2005 11:35PM)
The Neilson bottles aren't latex anymore... they're vinyl.

You can find a similar material that's clear or translucent urethane... but you don't' use plaster molds... you make the molds out of silicone..

the whole process isn't that complicated.. but needs to be done by someone that knows how.

I work in the FX industry in Los Angeles... and I do this stuff all the time.. get in touch!

Mike
makeupguy13@yahoo.com
Message: Posted by: olivertwist (Dec 7, 2005 08:04PM)
Also check out The Compleat Sculptor at http://www.sculpt.com/. If you are near NYC they offer classes in moldmaking.
Smooth-On also has videos you can but.
Message: Posted by: FrankBenning (Dec 8, 2005 08:25AM)
I've worked with this stuff off 'n on since about 1967...and there's some good advice given on here!!

One thing though, after you've cast anything in latex, make SURE and sprinkle some baby powder on it and rub it around so it doesn't stick to itself when removing whatever it is from the mold!!

Freshly cured (dried) latex will stick to itself like its got rubber cement or contact cement on it if not "powdered" before removal and make it unusable!!

Doesn't take but a light dusting but it sure HELPS in handling the finished casting!!