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Rubber Molds & Green Stuff

Technically the title of this post isn’t entirely accurate but I’ll get to that in a bit.

Any one who’s read my previous posts will have come across my use of Blu-Stuff putty to make simple push molds and simple Green Stuff casts. Whilst I’ve found this immensely useful there are limitations. Because the Blu-Stuff mold isn’t very flexible it’s quite difficult to cast anything really three dimensional and as such most of my uses have been replicating surface details.

The answer to this is to cast with conventional silicone rubber and resin, allowing complete 3D replication. My two main gripes with resin casting  are the time frame with the silicone rubber curing and the general toxic nature of resin. When I managed to acquire a material I called Liquid Blu-Stuff it solved the issue to a long waiting time as it cures within about 20 minutes.

I’ve had some successful casts using this and resin, but my general unwillingness to use resin unless absolutely necessary has meant I rarely use this technique. What I really wanted was a quick and simple way to make Green Stuff casts but I couldn’t make it work with the Liquid Blu-Stuff because the Green Stuff was too firm.

So last week I came across a 2 part putty called Magic Sculp on eBay that advertised itself as finer than Mulliput (link here) that I figured I’d try it out as a Green Stuff replacement. I’ve never really been a fan of Mulliput and so haven’t used it in years. This product smells just like Mulliput and whilst I can’t offer a proper comparison, I didn’t find it suitable for miniature sculpting. So I put it to one side and never expected to use it.

Then I remembered being told of how some people had tried mixing Mulliput and Green Stuff (something I’d never tried because of my dislike of Mulliput). So I tried mixing this Magic Sculp with Green Stuff (in equal amounts) and I have the admit that I was really pleased with the results.

The mix is softer than regular Green Stuff and using clayshapers I managed to get some very smooth finishes, far smoother than normal. When using spit or water as a lubricant there is a small amount of residue from the Magic Sculp that ends up on the chapshaper when sculpting, which makes it a little messier than plain Green Stuff.

Getting back to casting… it suddenly occurred to me that this mix is softer enough to push into a Liquid Blu-Stuff mold without distorting the mold.

So long story short, I found a really simple easy way to duplicate components in putty. I suppose just using the Magic Sculp without the mixed in Green Stuff might work too, but overall I think mixing the two different putties results in a much more suitable material.

Moving on…

My first test piece uses the torso and arms from a Reaper Barbarian miniature that I bought ages ago and never got around to using. I wanted to try and use this torso on the plastic Bestigor models to try and give them a move muscular look. As you can see it’s a very nice chunky piece and I hope a nice fit for my Beasts.

After selecting what I wanted to cast I took a small pot big enough to fit the piece with room for a reasonable thickness of silicone around the outside of the component. I used a small piece of poster tack to attach it to the bottom of the pot. Knowing the pot to be about a 30ml volume I then took a small measuring pot.

I added 15ml of the blue half of the Liquid Blu-Stuff to the measuring pot, followed by 15ml of the white half. I then mixed thoroughly with a wooden stick until it was a consistent light blue colour.

Next up I slowly poured the mix into the bottom of the pot. At no point do I pour directly onto the component, instead I let the pot fill up from the bottom until the component is fully covered.

After giving the Liquid Blu-Stuff 20 minutes to cure I removed it from the pot, and making my best guess used a sharp scalpel to cut open the mold, trying to slice the mold open down the center line of the component (where you’d expect the mold line). I had intended to cut it all the way through but I found I could remove the original component without completely separating the two halves.

Next up, I cut holes in the top and bottom of the mold, connected to the hands, bottom of the torso and neck of the miniature. I also cut corresponding hole into the bottom of the original pot just as I would if I were going to fill the mold with resin. The plastic pot and the fact the mold is still in one piece rather than two mean the mold will go back together accurately.

Moving on to the putty mix. I mixed equal amounts of Green Stuff and Magic Sculp, trying to estimate that I had a bit more than the actual volume of the original component. I have tried altering the ratio of these putties but I personally find a 1 to 1 ratio to give the best feel. I invite you to experiment if you wish to try this yourself.

After mixing I simply push the mix into the mold making sure all the negative areas are filled. I then forcefully pushed the two sides of the mold together. The putty is soft enough that with enough force the excess mix is forced out of the holes perviously cut into the mold.

The mold is then pushed back into the original pot to force the mold to hold its proper shape and put pressure on the soft putty inside.

I left this overnight. I’ve so far forgotten to time just how long this mix takes to cure. The Green Stuff is normally 3-4 hours whilst Magic Sculp is roughly 12 hours, so I’d estimate about 8 hours for this mix.

The next morning I removed the mold from the pot and very easily opened the mold and removed the cast.

As you can see the level of detail in the cast is very high and there are no air bubbles (I also did a cast in resin and did get air bubbles). The flash around the edge is about half a millimetre thick. This is dependent on just how much excess putty is used and how much pressure you can add when squeezing the two halves of the mold back together.

Another advantage to the Green Stuff & Magic Sculp mix is that it is a lot nicer to cut and carve than just pure Green Stuff. I can’t say for sure whether Magic Sculp is equivalent to Mulliput or not (it smells the same) but I assume it is.

Next post I’ll show how I put this to use with my Bestigor prototype.

May 21, 2012

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  • Steffen

    Looks really effective, how hard is the final cast compared to regular cured green stuff? And btw, isn’t green stuff toxic ?? I surely seem to remember reading several places that it is important to wash hands after using kneadite as the epoxy in it is not very healthy to you? 🙂

    • Seems to be harder than plain Green Stuff once cured.

      Well all epoxies are pretty toxic, but what isn’t these days. Personally, I can’t be using gloves whilst mixing/using this stuff so I am constantly washing my hands (I’m a little OCD when it comes to hand washing).

  • Jack Straken

    Impressive, the result looks comparable to what I got with the Sylmasta resin casting starter kit, but without the air bubbles and the hassle of mixing resin that isn’t 1:1. Will you be casting your Primarch masters with this process at any point? I’d love to see if it can pull off a whole leg+torso set  when there’s a few undercuts to worry about.

  • AekoldHelbrass

    How do you think, is it possible to use liquid and firm blu-stuff to make sharper parts with pure green stuff? Making first firm layer with blu-stuff, then filling everything with liquid-blu-stuff to hold blu-stuff from breaking?

  • alejandrinus

    Did you tried using plaster of paris instead of green stuff to make the cast? Im thinking for scenary pieces with liquid blue stuff.

    • I have and it works just fine.

      Shooting myself in the foot by saying this, but for large pieces you probably want to use a more conventional silicone rubber, simply because of cost. The Liquid Blu-Stuff is best suited to small projects because it can be measured in such small amounts and cures very quickly. Regular Silicone Rubber is always messier to use too.

  • can the liquid blu-stuff be reused, because it looked like you used a lot there, for such a small part

    • No the Blu-Stuff can’t be reused to make a different mold, although it can be used to make a LOT more of the same cast.

      This particular mold used just 34g of Liquid Blu-Stuff (about 1/6th of the 200g product). The mold could have been made smaller, it’s simply an issue of having the right size container to pour into (Lego is ideal).

      The advantage of Liquid Blu-Stuff over other silicone rubbers is that it can be mixed in such small quantities, with no mess. Regular RTV silicone rubbers require measured amount of catalyst (ie: 8 drops per 100g, or something similar), requiring weighing scales and usually 12 hours to cure.

  • spyke13

    I recently got hold of an old Eldar Harlequin jetbike and tried using Instant mold sticks to cast a duplicate of the canopy for another project. The instant mold did not seem to pick up all the detail. After reading your article, it appears that liquid blu-stuff may make this easier and does pick up all the details too.
    Thanks for writing this article – it’s been a great help!

    • The Liquid Blu-Stuff will definitely pick up the details. I assume it’s the grinning face canopy you’re speaking of. If you do the casts in putty (Mulliput and Green Stuff would be my recommendation, or just plain Mulliput) you should be able to do them with a one piece mold, as the inside of the canopy is generally hidden from view.

      • spyke13

        Yes – it’s the grinning face canopy. I was planning on mixing the blu-stuff and placing the canopy face-down into it in order to get a one piece mold. Would this work, or would I be better in pouring the blu-stuff over the canopy?

        • If you place it into the Liquid Blu-Stuff you risk getting air bubbles on the details. If you go that route you may want to brush the liquid over the details first to be sure it properly covered (be quick about it though).

          If I were doing this cast I’d make a small box from plasticard or lego and put plasticine in the bottom. I’d then push the canopy into the plasticine and neaten it up leaving the face facing upwards.

          So something a little like this: http://masteroftheforge.com/wp-content/uploads/2012/05/moldexample.jpg

          Then pour the Liquid Blu-Stuff slowly, letting it gradually fill up the container, but without pouring directly onto the component. This will make air bubble very unlikely, and give you a one piece mold into which you can push Mulliput or a Green Stuff/Mulliput mix.

          The easiest option would be to do it like I have in the above example, to simply fill the whole container with Liquid Blu-Stuff (with the component inside but no plasticine filler) and cut the rubber mold in two after.

          • spyke13

            The plasticine/box combo looks to be a good idea. As the canopy will be used for a Wraithlord head, the one piece mold would be better as I don’t want to risk cutting through the details in mold.
            I’ll just have to find some lego (shame I sold all mine years ago) and plasticine which should be cheap enough.

          • The Lego I got for my mold box was bought directly form Lego.com and I believe cost me just over £10, probably cheaper than trying to find second hand blocks.

          • spyke13

            I’ll have a look on ebay as I don’t think my younger cousins will be willing to part with theirs 😀

  • I followed this tutorial to the tee, but my results where no were near yours. Im doing an astral claw forgeworld shoulder pad. any ideas on what i may be doing wrong? should i use a different container instead of the one provided to me by blu stuff?

    • Hmm… any chance you could email me pics of the results you’ve got so far?

      A smaller mold container might be better. I’ll have a go at a shoulder pad myself tomorrow and see if I encounter any problems too.

  • Bob

    Is Magic Sculp the same thing as Magic Sculpt?

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  • matt woods

    Hey mate.  I was just wondering if you could use Green Stuff just by itself, without the Magic Sculp?
    As i am just having trouble getting hold of some Magic Sculp in Australia.
    Any help you could give me is greatly appreciated!

    • Sorry for the late reply I only just realised I’d not answered this.

      Green Stuff by itself will most likely prove to be too firm, and therefore push on the mold rather than the mold push on the putty (I hope that makes sense).

      I’d try Mulliput instead of Magic Sculp, it’s probably more widely available and from what I’ve heard gives the same “softer putty” mix when added to Green Stuff.

  • Great article, and pretty much what I needed for my own conversions. Quick Q: Is it worth wrapping the mould in a rubber band overnight, or do you just leave it be?


    • Yeah that’s certainly an option. I like to push the mold back into the container I made it in as then it pretty much has to conform to the correct shape. But a rubber band would work too.

      The main thing is getting the amount of putty used for the cast just right. You can often check after you first squash it in there and you’ll be able to tell if there are gaps in the cast (too little) or a lot of flash (too much).

      Of course because it’s putty you can just take it out, adjust, and squash it back in.

      I’ll have some more examples soon, as I’m tempted to cast up my own collection of Truescale Space Marines using this method and really test how far I can take the material and figure out potential problems.

      • Thanks for the reply. One more thing I forgot to ask last night: You obviously don’t cut the whole way through the mould, but how deep is the cut? About 300 mm from the bottom end enough?

        • No problem.

          The thing about the cutting is that it is totally dependent on the part and size of the mold (300mm? typo right?).

          You could just cut right through and make a 2 piece mold but then its more problematic to align afterwards.

          When I make the cut it isn’t just one deep cut and done, but a series of gentle cuts, all the while teasing the two halves apart.

          It’s not easy to describe accurately so I’ll try and make a video soon. Really you’re just trying to open it up enough to get the putty inside, the smaller the cut the better.

          I think some people are struggling in finding where to cut too. As long as the mold isn’t too chunky you should be able to feel the edges of the component in the mold when you squeeze it. Then it’s just a bit of guess work. Wherever the cut is located will determine where your mold line will appear on the cast.

  • Brandon Burt

    Smells the same -shrugs-

    • It’s a good indication that the materials use the same chemicals. At least that’s how I see it.

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