Question about molding from plated or painted parts

[Ryan S.]

I've recently got a resin casting kit from Alumilite to try my hand at casting some parts. My question is, can a mold be made from plated or painted parts or is it best strip them and make a mold from the bare plastic piece?

Thanks for any advice!

Edited December 24, 2015 by Ryan S.

[Mark]

When you make a mold of a painted or plated piece, you are casting parts with one or more layers of paint or plating built in.  When you paint the castings or have them plated, you end up with a double layer.  Better to start with a bare piece whenever possible. 

[Ace-Garageguy]

Mark is 100% correct, and to elaborate on what he said...every layer of material that's put on over the bare plastic (paint or plating) softens details. If you take a mold from a part that already has the details slightly softened, make a part from that mold and then primer / paint or plate it, you'll have even softer, blurrier details. It's like making a Xerox of a Xerox of a Xerox...eventually it becomes unreadable. The people who make the best masters and castings take this stuff into consideration.

Another potential hazard with molding from painted or plated parts is that the paint or plating may decide it likes sticking to the mold better than it does to the original part. It's very difficult to clean stuck contaminants off of the inside of a mold....especially in scales like 1/24 and smaller...without damage. While it's true that this usually happens if the part surface isn't properly prepared with the correct release-agent prior to making a mold (or if the paint or plating isn't very well adhered to the original part) it's always a possibility.

Edited December 24, 2015 by Ace-Garageguy

[Mark]

I always tried to have little or no primer on any of the kitbashed/fabricated parts I used as masters.  Nothing at all (primer, paint, plating) on parts that I was copying with no alterations.  It isn't so much the plating as it is the lacquer undercoat that is applied in order to get the plating to bond to the plastic.  That stuff can get thick, and tends to be even thicker in recesses or corners.  Just get rid of it, and cast the part exactly as it was molded originally.

I did cast a couple of bodies years ago, and that applied to those as well.  A lot of guys creating a body or hood master will take three swipes at it with the sandpaper and start blasting several coats of primer onto it.  They're only fooling themselves...the mold material will warm up just a bit during the curing process...just enough to shrink the primer and reveal a bunch of sanding scratches in the surfaces of the part, reproducing them in that mold (and every part cast from it).  To this day, when I do bodywork, I apply primer with a brush only to the areas where work was done.  The rattle can doesn't come out until bodywork is finished, and the painting process has begun.

[Ryan S.]

Great advice and your points make a lot of sense for getting a clean, crisp mold. Thanks Mark and Bill. I'll keep this in mind when I start playing around with the molds and casting. 

Cheers!

[dimaxion]

I delayed  casting myself for a long time . As such the questions I did ask Professional Casters in 2011 about . It was what filler on the Master will withstand being removed from the Form attached to the Form . A huge problem Problem in the early days of Casting seems to have past into History with today's Casting / Mold Making Materials . . IIRC , this may be a concern using cheap RTV for Molds still today . As the type for Automotive gasket making I am referring to . I use it on occasion for small parts . Thanx .. .

[Art Anderson]

I always tried to have little or no primer on any of the kitbashed/fabricated parts I used as masters.  Nothing at all (primer, paint, plating) on parts that I was copying with no alterations.  It isn't so much the plating as it is the lacquer undercoat that is applied in order to get the plating to bond to the plastic.  That stuff can get thick, and tends to be even thicker in recesses or corners.  Just get rid of it, and cast the part exactly as it was molded originally.

I did cast a couple of bodies years ago, and that applied to those as well.  A lot of guys creating a body or hood master will take three swipes at it with the sandpaper and start blasting several coats of primer onto it.  They're only fooling themselves...the mold material will warm up just a bit during the curing process...just enough to shrink the primer and reveal a bunch of sanding scratches in the surfaces of the part, reproducing them in that mold (and every part cast from it).  To this day, when I do bodywork, I apply primer with a brush only to the areas where work was done.  The rattle can doesn't come out until bodywork is finished, and the painting process has begun.

To further advise on this:   RTV Rubber does, in my extensive experience, tell the story of the surface of whatever master is being used to create the mold, even better than a camera does!  By all means, strip all plating, even the "wet look" gloss coating that gets used before the plating is done--you will be surprised at what all that stuff hides in the way of surface details.  At the same time, get rid of all mold parting lines, as those just interfere with what otherwise could be a great casting.

When using putties and primers on bodies to be used in resin casting, take the time to polish that out to as nice a shine as possible--the better you do that the nicer the casting!

Art Anderson

[Joeys Models]

Should not be a problem. The silicon rubber has a shrink factor to it. Usually .001 to .003 . Worse if it's cheap rubber like Alluminlit. Check their website for spec. on there resin. With painted parts and plated. In my experience will not effect the casting. I usualy prime all my parts before I mold them.

[Steven Zimmerman]

I have made literally hundreds of molds , and have never stripped the chrome from the masters I used. I have never had the chrome lift - in fact I prefer to use parts already chromed.....'Z'