Cold Casting: What am I doing wrong?

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Ein

Sr Member
RPF PREMIUM MEMBER
I always powder my molds with the metal powder when cold casting. Yes, it will take the "gloss" away from your cast, but it doesn't prevent it from being polished
Yeah, when I say I'm 'powdering the molds', I mean with the same aluminum I'm casting with.
 

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cavx

Master Member
I always powder my molds with the metal powder when cold casting. Yes, it will take the "gloss" away from your cast, but it doesn't prevent it from being polished
I understand why one talcs a mold. The parts release easier and it extends the length of the mold. As we both know, silicone is not cheap, so we want to get the most life we can from them.

Yeah, when I say I'm 'powdering the molds', I mean with the same aluminum I'm casting with.
Talc is pretty fine, but is the this aluminum powder as fine or more course? If it more course, then it will be roughing the surface of each cast.
 

Risu

Master Member
RPF PREMIUM MEMBER
I can't speak to the 200 mesh, but I've got some 400 mesh aluminum powder and it's about as fine as flour. I've actually had some of the same problems with my cold casting, so I've been following this thread. My problem is that even the lightest polishing with steel wool goes right through the aluminum powder and exposes the resin mix underneath, which doesn't look metallic at all.
 

AtrumAntics

New Member
iv had a similar issue cold casting with bronze powder the powder itself if 400 mesh which is super fine but like Risu when i polish it i seem to polish straight through the powder despite using the 1:1:1 mix ratio i'm also using onyx fast and this sets of to quick to degas and using a syringe to get it into my mold quick as it was to thick to pour in before the flash-off point
 

kwalsh0000

Sr Member
RPF PREMIUM MEMBER
I have always dusted the mold and then done a light coating of resin with powder (just a light one to back the dusting) before the standard tinted resin.
The helmet there was just done with 00 wool and is weathered (not even 0000 or metal polish to give it a shine) so dusting a light coats still keeps a shine. Maybe try lighter coats?
 

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Luke0312

Sr Member
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I understand why one talcs a mold. The parts release easier and it extends the length of the mold. As we both know, silicone is not cheap, so we want to get the most life we can from them.



Talc is pretty fine, but is the this aluminum powder as fine or more course? If it more course, then it will be roughing the surface of each cast.
You dust the mold to assist with wicking the resin into all areas. I'm not even sure it assists with extending the life of the mold, the best thing to use for that is mold release,.

Even if the aluminum powder did cause a slightly rougher surface, you're polishing it afterwards, so that wouldn't make a difference.
 

Ein

Sr Member
RPF PREMIUM MEMBER
My goodness, I just had a go with using Onyx Fast and barely even had time to get the mold filled. I have no idea how you guys are doing this. Those of you using Fast, are you working in open-faced molds or something? The things I'm generally trying to cold cast are at least two-part molds.
 

Zombie Killer

Sr Member
RPF PREMIUM MEMBER
Wouldn't it be better to mx the aluminum into part A or B only? Then you can take your time degassing before mixing. I find most of the bubbles come from the resin manufacturing process and not from mixing unless your going crazy mixing. Onyx has always been a pain for me to use do to its super fast setting time. I'm very interested in this thread too, I have some 200 mesh powder from Smooth on to try on my MIB pulsar but this is all new stuff to me. I think I have some onyx around here somewhere I need to try some test pieces. If I can get close to what Kevin Gossette posted I will be happy. Nice stuff Kevin!
 

Kevin Gossett

Master Member
RPF PREMIUM MEMBER
Thanks!

With the Onyx Fast, I have enough time to mix and pour into 4 different molds, 3 of which are just simple open-face and one two-part mold (belt buckle). If you're finding that you don't have enough time for a single pour, chill your resin in the fridge prior to using it. That will give you some extra working time.
 

Circassian

New Member
Hi everybody

I have a big problem about blackening my cold cast bronze objects

There are a few spotty parts on my cast after laying down the cast in black patina liquid you can see the picture below

http://www.dosyaupload.com/4Qnx


If you can help me about this I would be very happy
Am I doing something wrong ?
 

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robstyle

Master Member
Hi everybody

I have a big problem about blackening my cold cast bronze objects

There are a few spotty parts on my cast after laying down the cast in black patina liquid you can see the picture below

http://www.dosyaupload.com/4Qnx


If you can help me about this I would be very happy
Am I doing something wrong ?
That link is either click bait or being misread by my browser. Either way, an older thread that could still use some info.

Keep in mind I do not use Smooth On products, and the following is based on my own experience and others ive seen first hand. I cant speak for the lucky ones that have had success with the prior mentioned methods and materials.

With metal powders the mesh number, in this case 200 and 400, just isnt the best for the task. I may be wrong but I assume the reason 425 mesh metal powders are the most commonly sold by retailers is due to its mesh size alone. The finer the powder (mesh) the more airborne it becomes and the need for expensive respirator systems is needed. My assumption is 425 mesh seems to be less likely to cause "lets sue them" circumstances.
Ive tried numerous times using various metal powders in the 325 to 425 mesh, cold casting, brushing into the mould, mixing into A or B or both.... Ive had no real success with various materials. The only real success I have seen first hand with 425 mesh powders was when the casting material was clear polyester resin tinted black. Basically surfboard resin. Then steel wooled for the metallic sheen to shine through. The issue with casting resins is the inherent soft surface combined with the cure process. To get the sheen you need to scratch the surface. For the material to cure it pushes the metal away...

I use MPK90 in black. Its a high impact and fast curing plastic. But its also expensive. In the end I know what works by trial and error. Why try and save a percentage in materials when you lose that in trial and error with lower cost materials? I also relegated 425 mesh metal powders to castings that would need to have a magnet attached. For metal powders I use industrial grade in the 10,000+ mesh. When you get into what the term "mesh" means, thats an incredibly fine number. So fine in fact when my lungs were pumped a few years ago from a fluid build up there looked to be a T1000 lurking in the fluid. Once that metal gets into your lungs, it only comes out in death or happenstance such as having your lungs pumped. For an idea of what that metal powder handles like, its like running a felt tip marker over paper, yet its powder. The outcome is no need for steel wool and perfect castings every time. I have tried to explain the process to a couple people but they had no success. Again I use a tried and true material, they used another brand. I wont get into casting in color as I cant for the life of me type that out. Ive even done in in front of an experienced mould/cast person and they were dumbfounded.

Some examples of castings:

Strait from the mould knives with the original, cast in color:


Strait from the mould badges and brass knuckles:


Transformers badges, completed but again, no steel wool, just a black wash.
 

FoamSmith

New Member
Also, I've been pressure-casting my casts in order to eliminate bubbles - getting a pitted surface on a cold-cast seems irreparable, because there's no way you can fill in the holes with anything that won't also have completely ruined the metallic surface. How do you use Onyx Fast without air bubble issues?
.
You can fix bubbles in cold cast parts. Use the old CA trick but with your metal and not talc. Keep in mind that the repaired section will be shinier when polished since it is almost entirely metal.

Coldcast Repair.JPG
 

razorsharp192

Sr Member
RPF PREMIUM MEMBER
Whenever i've moulded metal parts, I always do 1:1:2 so the aluminium powder is equal to the total amount of resin, never had any issues. Alternatively have you tried aluminite metal powder? they work great.
 

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