Pewter casting help

[Sevv]

I’m currently casting parts for a prop in pewter and I’m coming up against some hurdles I was hoping someone on here could help me with please.

Ive searched the RPF and found some information from 2008 which said to heat the mould first to try to equalise the temperature but unfortunately that hasn’t helped.

When I cast I get areas of my cast that are lovely and shiny. Just what I want. I also get random areas of my cast that are very matt, almost speckily in its surface quality. It’s these areas I am trying to avoid. As you can see from my image above.

Pretty simple set up. Mould cast from Mold Max 60. One part mould. Lightly talc the mould as a release. Heating my pewter in a stainless steel pan with a blow torch. Remove the top layer and pour in. Leave to cool. The pewter is from here:

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Seems good quality stuff. I don’t really get it. The first test mould cast I did was fine, since it’s seems totally random if I get this surface quality and how large it is.

Any help would be appreciated

Thank you

 

[Cbstudios]

I've done a decent amount of pewter/low temp alloy casting with similar products to what you're using, and I too find a very similar surface texture happens on a lot of my casts.I usually tend to sand the defects out, but two thing I do for more consistent results is pre-heat my mold (as you said) for around 10-15 minutes at 210 degrees F or about 100 degrees celsius. I also dust my moulds with graphite powder and a really soft make-up brush. The silicone I use is M4470, with a high temperature resistance and a 60A shore hardness.

Its super important that your release powder is dry as it can be, as it WILL cause bubbles and pitting, which is why I prefer graphite as it tends to hold less moisture than talc. Pre-dust your mold before you heat it so it'll drive as much moisture out before you cast. Hope that lends a machete to your intellectual thicket.

 

[DaveChaos]

I cast daily with Pewter so hopefully I can help you a little. It Sounds like your setup is ok but what does your mould look like? If you have made a pour in mould, how big is your inlet? The reason I ask this is because you need some weight behind what you're trying to cast to capture all the details so the inlet should be the same size as your model.

Fresh baby powder I find works well but you can also use a fine graphite powder. You're no likely to get a instant shiny model they will always come out dull.

Looking at your picture it looks like your model is thin? if this is the case it could be that its cooling down too fast when you cast, I find smaller models need a little more heat. I pre-heat my mould to 110c.

 

[Sevv]

Thank you very much for the help both of you. I've already ordered some graphite powder and looking at implementing all your suggestions on my next cast. Yes it is fairly thin 15mm down to 7mm at its thinnest. It has an open back to the mould. imagine 5 sides of a box with the 6th side open and that's where I pour the metal in. Is that a bad way to go? Should I have an enclosed box with a small hole for pouring? Any tips on how I can prevent it cooling down so fast once its poured?

Plan on doing another cast tomorrow when the powder turns up. Ill post an update afterwards and let you know how it went. Ill post some pics of my mould etc then aswell.

 

[Cbstudios]

I cast daily with Pewter so hopefully I can help you a little. It Sounds like your setup is ok but what does your mould look like? If you have made a pour in mould, how big is your inlet? The reason I ask this is because you need some weight behind what you're trying to cast to capture all the details so the inlet should be the same size as your model.

Fresh baby powder I find works well but you can also use a fine graphite powder. You're no likely to get a instant shiny model they will always come out dull.

Looking at your picture it looks like your model is thin? if this is the case it could be that its cooling down too fast when you cast, I find smaller models need a little more heat. I pre-heat my mould to 110c.

View attachment 1486594

DaveChaos That is some super nice looking mold work, I gotta say!

 

[DaveChaos]

DaveChaos That is some super nice looking mold work, I gotta say!

Thanks!

Thank you very much for the help both of you. I've already ordered some graphite powder and looking at implementing all your suggestions on my next cast. Yes it is fairly thin 15mm down to 7mm at its thinnest. It has an open back to the mould. imagine 5 sides of a box with the 6th side open and that's where I pour the metal in. Is that a bad way to go? Should I have an enclosed box with a small hole for pouring? Any tips on how I can prevent it cooling down so fast once its poured?

Plan on doing another cast tomorrow when the powder turns up. Ill post an update afterwards and let you know how it went. Ill post some pics of my mould etc then aswell.

IMO I would make a two part mould, its better at retaining the heat.

I find temperature is key, I know there is a general best working temperature but every mould in my experience is different. Here is a extreme example. This model is about 1mm or less is some parts, Pewter really doesn't like to get into such a small space with just gravity alone. So I had to turn up the heat to get more flow. The mould was heated to about 230c and the Pewter is closer to 400c. where as the mould in my previous post I don't pre-heat at all as the model is quite large.

 

[robstyle]

I see graphite powder has already been mentioned.

On a side note, one trick you can use to test castings without having to deal with metal, Crayola Crayons. Literally melt them in a soup can, and pour. Ive done lots of test castings as well as props for film use with Crayola Crayons. Not sure exactly why that brand works everytime, could be the wax content as other brands split of break in the mould. Ive cast things as small as a coin to as large as a pistol with no issues.

 

[PoopaPapaPalps]

I'm a bit of a novice in comparison with some of the people here who've given advice, but in my experience, heat with pewter is always a factor in getting good fills. Especially on smaller pieces.

Pewter shouldn't get so hot to the point where it turns yellow/purple but it should be hot enough to stay liquid a little bit longer after being poured into the mold. After pre-heating and dusting, pour the metal in until your vents fill or whatever, and then tap your mold a few times along the edge to help get bubbles out and to help the metal fill in the negative properly.

 

[Sevv]

Unfortunately I’m still not having much luck. I’ve remade my mould, made from Mold Star 30 as that’s what I had left over in the workshop. 2 part. Nice and chunky.

I’m heating it in the oven at 210 degrees for 20 mins before I cast. I’m now using graphite powder as you can see. As it’s a 2 part mould I would hope it’s cooling slower as it should retain the heat better. Pouring hole is about 1cm. The metal is nicely getting into all areas of the mould. I wouldn't have said my metal is getting too hot. Its not turning different colours or anything before I pour it.

Still getting the same results shiny in places but that horrible matt texture in, I’m sorry to say, most places.

I want to say I’m over thinking this and I just need to buff the finish out but... I have tried buffing one. Unfortunately all it did was emphasise the blobbily nature of the finish.

The other thought I had was, I’m re melting my failed attempts and re pouring the same metal over and over again. Is that a bad idea? Does the repeat use make the metal worse in anyway? If I bought some new pewter might I have more success?

edit - it might be a coincidence but I've just tried a few scraps of pewter that I've only reused once since I got this batch and the cast has come out much better. I'm going to buy some more and try some new pewter.

 

[PoopaPapaPalps]

I've never had a problem re-melting pewter scraps. Any matte areas I've found I could sand out.