Cold cast metal - metal powder ratios and resin tinting?

sumghai

sumghai

New Member
As part of my ongoing Star Trek Online Starfleet uniform project, I'm making a set of combadges and ranks pips via cold casting with Smooth-On products.

The badges and pips are golden brass for the 2409 version and silvery aluminium for the 2410 version. Due to their small size, shape and the use of two-piece silicone molds, I'm thinking of doing a solid resin/metal fill rather than just a gel coat, but I'll definitely dust my molds in metal powder first to further improve the lustre.

In order to get the desired bright* golden brass and silvery aluminium effect:

- What ratio of resin part A : part B : metal powder should I use? 1:1:1, 1:1:2, 1:1:3 or more?

- Is it necessary to tint the resin? If so, what color?

- If the tint is black, would it be better get Smooth-Cast Onyx (which is already black) or Smooth-Cast 325 with the appropriate colorant?

Advice, suggestions and accompanying photos would be greatly appreciated.


*I may weather these badges later on with black shoe polish
 
Whilst I have had success with mix ratios of up to 30% with Glow In The Dark powders, I believe you are only supposed to mix 5% per volume with tints or the resin may not cure.
If the resin comes in black, I'd buy that rather than mix my own.

Remember, these metal powders are heavy so they may settle on the bottom of the cast.
 
sumghai,
Having made some of these for First Contact, the way you want to do this is, dust your silicone mold with the powder and then pour the straight mixed resin in. The black resin will give a richer effect with metallic powders. The powder will fuse itself to the resin completely. We coat molds with powder by putting a tiny amount in the mold, then banging the mold against another mold or hand, but, covering the opening so the powder doesn't fly all over the work area. This aerates the powder, covering the interior of the mold evenly. then you want to dump out any excess powder. You only need a thin coating to work. You can also dust it into the mold with a soft brush. Although rare, make sure you powder has no carbon black in it. (This is sometimes added to powders to "darken" them) Since the carbon is finer and a different particle form, it will streak over the surface of the mold if you use a brush. Do not leave any clumps of powder (Like in corners) as this will keep resin from filling the mold.

If you want to mix powder into the resin, you have to add a lot to overpower the black tint in order to get the brightness the communicators have, so it would be better with neutral resin (white). The issue with adding powder to the resin, is you will often get "swirls" in the finish, as the material flows around the mold. The finished cast will also not be as bright as the surface coated cast because the powder is mixed into the resin.
 
Thanks lmgill.

As I stated in the OP, I was already planning on dusting my molds with metal powder first, then fill with the resin/powder mix.

What resin to metal powder ratios do you use?
 
If you dust the molds, then putting powder in the resin is a waste. Since the powder on the surface will have a completely different look than the powder in the resin, a scratch in the surface will still show up, powder or not. If you feel you have to mix it in, then experiment with perhaps 5% and add more if needed. But the resin will kill most of the luster.
 
Cold casting (metal powder mixed into the resin) is great for things that should have a worn metal look - for example, Rubbertoe's Doctor Who props often are done this way.

If you are going for the shiny new Starfleet look, pigment (not metal) powder brushed/shaken into a mold before casting will provide a more appropriate result. Though I see you are planning to weather them, so maybe it's not the traditional shiny Starfleet look that you want?

I've also noticed in my experiments with the process that a black tinted resin enhances silver pigment powder, and brown tinted resin is good for brass/gold pigment powder. Pro shops like Rubbertoe also use grey/black resin for their cold cast metal (mixed in) items, and brown tinted resin for brass/gold/bronze cold cast items.
 
E Williams said:
If you are going for the shiny new Starfleet look, pigment (not metal) powder brushed/shaken into a mold before casting will provide a more appropriate result. Though I see you are planning to weather them, so maybe it's not the traditional shiny Starfleet look that you want?
Click to expand...

You're correct - I'm aiming for a slightly weathered look. I suppose my use of the phrase "golden brass" was imprecise - I've seen cold cast brass varying in hue from yellow to murky browns, and I just wanted to avoid the latter.

E Williams said:
I've also noticed in my experiments with the process that a black tinted resin enhances silver pigment powder, and brown tinted resin is good for brass/gold pigment powder. Pro shops like Rubbertoe also use grey/black resin for their cold cast metal (mixed in) items, and brown tinted resin for brass/gold/bronze cold cast items.
Click to expand...

This was what I was looking for! Thanks!

Daniel Nelms said:
I mix equal parts resin and metal 1:1:1 and tint the resin black. I used MPK resins.
Click to expand...

I think Smooth-On also recommended a 1:1:1 ratio for their products as well, although some folks have used even higher ratios.

Since these badges are fairly small and thin, I'm reasoning that a high metal powder content won't be too costly per item.
 
I'm curious to see what this pice looks like, as I have never used that much matalic powder in a casting.
 
One thing to keep in mind if you're just powdering the mold and not adding metal powder to the resin, is that if you're mold doesn't have a pour spout, the initial splash of resin may displace the powder on the surface of the mold, leaving you with a casting that is metallic with a dark resin spot where the resin first hit the rubber. I've had it happen on several of my castings, and the only way I found to minimize this was to add a bit of metal powder to the resin. Since the metal is heavier than the resin, it will sink down to the bottom of the mold, which is the top of the casting. I found that I didn't need a lot of metal powder in the resin, but it did need some.

My castings were all open face one part molds, If yours is a two part mold, then you may not have that problem. Just my two cents.
 
Collektor said:
One thing to keep in mind if you're just powdering the mold and not adding metal powder to the resin, is that if you're mold doesn't have a pour spout, the initial splash of resin may displace the powder on the surface of the mold, leaving you with a casting that is metallic with a dark resin spot where the resin first hit the rubber. I've had it happen on several of my castings, and the only way I found to minimize this was to add a bit of metal powder to the resin. Since the metal is heavier than the resin, it will sink down to the bottom of the mold, which is the top of the casting. I found that I didn't need a lot of metal powder in the resin, but it did need some.

My castings were all open face one part molds, If yours is a two part mold, then you may not have that problem. Just my two cents.
Click to expand...
Interesting,
What type of powder you are using? Also, what type of silicone?
Because in 30 years I have never had this happen. We have used both tin and platinum based silicone and the powder is a very fine powder.
 
lmgill said:
Interesting,
What type of powder you are using? Also, what type of silicone?
Because in 30 years I have never had this happen. We have used both tin and platinum based silicone and the powder is a very fine powder.
Click to expand...

Admitedly not the good kind. I generally use Oomo 30, and the metal was copper powder, both bought from Smooth On. I noticed the blank spots in the castings were exactly where I'd poured the resin, pouring both fast and slow. I also put enough powder in the mold that I had to tap out the excess back into the container.
 
As a rule, we only "dust" the surface, never leaving any excess in the mold.
Here are some Apollo spacesuit fittings, cast in urethane with a metallic blue powder. Only the surface is dusted and I think the resin is black.
IMG_2072.JPG
 
I think some of the confusion in several posts here is that Imgill is describing metallic pigment powder (like Jacquard Pearl-Ex or Smooth-on Cast Magic) while Collektor is talking about actual metal powder. Two very different things.

Pigment powder will stick to and coat the mold much better than metal powder and will provide results like Imgill posted. No polishing of the casting is needed. It would be useless and wasteful to mix pigment powder into resin.

Atomized metal powder can be mixed into resin in high ratio, typically 1:1:1 with part a:b:metal. A high ratio like this forms a gel coat that would be brushed into a mold, not poured (metal powder is expensive!). Then that gel coat would need to be backfilled with plain resin, and once removed from the mold it would be polished with an abrasive to reveal the luster of the metal particles.

The actual metal powder can also be used to coat a mold, but issues like what Collektor describe may occur. In addition, if only the mold were coated without adding metal to the resin, polishing the dull casting to give it a metal shine would be difficult to do without rubbing through to the base resin.
 
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With such small castings is a gel coat needed ? I am looking at a Dredd Buckle in brass would you still recommend brush a 1:1:1 resin metal powder gel coat then when dry back fill with clear or black ? Resin or just do the whole thing in one cast.
 
Can I ask I sm looking at doing a Dredd Buckle would you still do a gel coat 1:1:1resin a-d and metal powder. Then back fill with black or clear resin or just cast the whole job in one. Plus if back filling do you wait for the gel coat to set. Total novive 1st ever casting. Note brass metal powder and I will be rubbing with wire wool after casting. Hence not dusting the mould ?
 

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lmgill said:
I was suspecting this was the issue. I have never used powdered metal in casting, so this makes sense now.
Click to expand...
Sorry to derail that very interesting thread folks...Imgill: since you don't have PM and asked for the type of match seen in the intro from "Mission Impossible" T.V. series...I believe they used a long match (to light a fireplace) for that intro. The way the hand is holding it, a regular match would be too short;) There! Back to our regular programing :whistle::whistle:

1689165534696.png
 
joberg said:
Sorry to derail that very interesting thread folks...Imgill: since you don't have PM and asked for the type of match seen in the intro from "Mission Impossible" T.V. series...I believe they used a long match (to light a fireplace) for that intro. The way the hand is holding it, a regular match would be too short;) There! Back to our regular programing :whistle::whistle:

View attachment 1718558
Click to expand...
Thanks. It was a bit of joke, in being an incredibly obscure prop, but being iconic at the same time.
 

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