Casting Home Casting: What products and methods do you prefer?

@Miss_Pygmalion Great idea! Perfect timing for me personally because I'm going to cast my first BJD head in very near future (still working on sculpt but it's approaching to completion). Looking forward to answers of more experienced fellows!

 

From my brief experince in mold-making and casting:
I've used local brands of silicone, but something interesting to consider is their shore, that is, how hard The silicone becomes once cured. A low shore silicone (from 10-20) is more than enough for casting with poliurethane resin. Using a release agent when casting increases the mold's 'lifespan'. I normally use vaseline during mold-making and talc for resin casting (applying talc every time I'll cast a piece).
About resin, the only poliurethane resin I've used is Smooth Cast's 320, can't say much about other brands. This resin cures very fast, taking 15 minutes to harden completely.
I've never tried coloring this resin, since becomes an Ivory-white color... might be possible, but not ideal. This resin can be used for pressure-casting, but I don't have the equipment to do so. I've used it for roto-casting (spinning and turning the mold to make a hollow piece) and it worked really well.

 

Not at all experienced but from my first attempt I learned that (for me) the longer the cure time the better if you're making a full doll, my resin had a working time of 10 minutes or so and it was never long enough, you have to work very fast to fill all the molds before it begins to set and becomes unworkable. Smooth-on resin with ease release works well, but I used oomoo for the junk mold and honestly wished I'd just bought mold max because it tore so easily and broke down so fast I didn't even get 5 casts out of it before giving up and discarding the molds. The oomoo also shrunk my 49cm doll down almost 1 cm which was significant.

I use a vacuum for the resin and it does help, but to be bubble free I really think a pressure pot is necessary. It's the next thing on my to buy list. I have a tiny one, but need much larger for 50cm dolls.

 

I’ve been using any old silicone, as long as it’s pourable. Resins are a different matter. I know smooth on do uv additions, but for my tests I used a general fast cast polyurethane. It cast nicely and cured fast. I then left one in the sun and.... whoa, yellowing is not the word. This thing went orange over one summer on a south east facing windowsill.(U.K. summer, I might add). That said, it also got a tiny bit of time in a uv light box. I’d be interested to know if anyone’s found a resin that yellows more slowly. If I ever did sell, I’d hate to send out heads or dolls that a year down the line look horrible! Hence I’ll continue with the yellowing tests.

 

i like smooth-on brand for silicones and resins! sortaclear 40 is my preferred mold making silicone, and the smooth-cast 320 and 325 resins are really nice! smooth on makes a really nice liquid pigment too! just be super careful with it, because it will literally never dry, and a toothpick sized dot of it can turn a load of laundry pink. 320 cures an opaque white like LilaAIP said, and 325 cures clear. technically 325 is a better resin for adding color because the color of the resin will not effect the color of the pigment. however, 320 is still great for adding pigment, it’s just difficult to color match. so, if you choose the 320 for pigmenting, make sure you write down your pigment recipe, or you’re never gonna cast a doll exactly that color again!

i’m not exactly sure what you mean by ‘most effective pot time.’ but i can say that pot times vary widely between resin types and brands. same goes for curing time. curing time can also change based on a number of factors, including temperature, humidity, and the thickness of your cast. the thicker the cast the faster the cure time, and the warmer the environment the faster the cure time. with a 1/4 inch piece cast in one of the smooth-cast 320 series resins, i would pull it out of the pressure pot after about ten to fifteen minutes, then let it rest under a heat lamp for another hour or so. it’s also a good plan to let it cool before you open the mold so that you don’t deform your piece.

i always recommend a pressure pot if there is one available. especially for moldmaking silicone. the harder silicones are going to pick up a lot of bubbles when you mix it, and without putting it in a pot you will never get all of them out. even using a vaccum chamber won’t fully degas a really viscous silicone, so i have found that using both creates the best molds. 42 psi is a pretty good place to start for pressurizing. it doesn’t take much. i don’t have much experience making molds without a pressure pot, so i don’t have any tips for working without one.

with sortaclear 40 i can get about 50+ clean casts before the mold starts to deteriorate! even when you use a mold release, chemicals from the resin leech into the mold and start to break it down. i will also say that using vaseline on some silicones is probably not a great idea. vaseline chemically breaks down the silicone and makes it more prone to tearing. i saw somebody literally tear a mold in half after some one used vaseline on it and let it sit for a year. that’s a long time, but making molds is expensive and difficult so it’s nice to be able to archive them.

and speaking of mold releases, i use straight up baby powder! just sprinkle some in and dump out the extra! you don’t really need mold release when casting urethane into silicone, because the two materials don’t bond.

sorry if that was kind of long winded but i hope it helps!

 

@Miss_Pygmalion as far as working time goes i like to fit my habits to the resin that works best for my project if that makes sense. after a few screw ups you can find a mold filling method that works for you, regardless of pot time.

i only put moldmaking silicone in vaccum chambers, almost never resin. pressure pots are not super effective for degassing pre-pour because the likelyhood of catching bubbles while filling your mold is high. so, my recommendation is to fill quickly and get it in the pressure pot right away. this is where having an extra set of hands is very helpful.

 

it honestly depends on how much of a rush i’m in. 2 part molds with keys cut in are definitely easier to make but take at least twice as long. i have also screwed up and not sprayed enough release, which sucks because you have to cut the mold open anyways. as long as you’re careful about that, like spray way more than you think you need, then freak out and spray a bunch more ! especially around the edges and in the corners!

jewel cut molds are hard to get a hang of. like really hard to do right. and everyone does it a little bit differently so it takes a lot of experimenting to find the way that works best for you. truthfully i am still getting the hang of it and tend to miss the line i was trying to cut along.

 

I'll be following this thread with interest. I've only tried casting a couple of times, and while it wasn't a total failure, it wasn't the greatest either. I had a lot of bubble trouble. Don't know if that was the materials, or operator error, but I suspect the latter.
I used this silicone Alumilite's High Strength 3 and this resin AlumiRes (RC-3) Tan . I don't have a vacuum or pressure pot, so I followed their suggestions for better casts, warming the molds and coating with talcum powder and so on. The resin had a very short working time, only 2 minutes for a piece as small as a head. It cured a nasty tan color. I'd probably try a different resin next time.

 

Following because this is something I'd love to do some day

 

@c4tbus thanks for the post, it's really helpful!
Why choose smooth-cast 320 and not 310 (I was considering the latter as the seller didn't provide technical information on 320)?

 

@Sillion the 320 series is easier to add pigments to than the 300 series!

 

@c4tbus Thanks! And one more question - do you use 320 or 322? As 320 seems to have only 3 minutes of working time.

 

@Sillion mostly because it’s cure time is only 10 minutes! i work with a lot of teeny tiny things, and the smaller/thinner your part, the longer it will take to cure fully. it’s also the strongest of the 320 resins (by only a fraction) but it does have the highest shrink rate. you can read the full details about the 320 products here!

https://www.smooth-on.com/tb/files/Smooth-Cast_320,_321,_322.pdf

i honestly recommend a little experimentation to find the product that suits your personal casting style the best ! there would be no harm in trying the 321 or 322 if you are looking for a longer pot time. for home casting dolls, the difference in the final product will be insignificant.

 

@c4tbus That's really interesting, that the smaller the longer it cures. I suppose a 1/3 head isn't that small. Well, experimenting would be the best - but expensive - the 0,86 kg trial package is still quite costly.

 

@Sillion a 1/3 head is a really easy size of thing to cast. when i say small i mean TINY !

it is because urethane resin heats up as it cures and that heat helps it cure, so if there is only a tiny amount, it can’t get hot enough to help itself cure if that makes sense. ( not real science, just how i understand it )

so something that takes two hours to cure at 1/4” thickness will take no less than 1,000 years to cure at a 1/16” thickness. ( true story from personal experience )

 

That makes perfect sense to me! And again, is very helpful - good to know!

 

Why is it easier to add pigments, can you see the final color when it's still liquid? (i assumed that's what the smooth-on info page means, but would like to be sure) I used the 300 series resin and it was really hard to know how it would turn out because the base white colour would only happen when it cured. Thanks for so much helpful info!

eta: oops, found my old receipt and in fact I used 322 resin, but it was still hard to know how the colour would turn out. I wonder if the 325 series would be easier, I'll probably try that next time.

 

@crowtree i honestly have no idea how the science behind it works !

but 325 cures clear with no pigment so if you are going for 100% perfect color match, that is your best bet !

 

@c4tbus thank you, I will definitely go with the 325!

 

@c4tbus Just to make sure before purchasing it - Sorta-Clear 40 works well with smooth-on polyurethane resins? Isn't it too hard for removing the doll head?
Thank you so much for sharing your experiences!

 

@Sillion yeah, sortaclear 40 is my go to!

i’m excited to hear that you’re pulling the trigger. can’t wait to see what you make!

 

Def following this thread as i wanba try n make a head soon

 

Very inspiring thread. I may try casting resin myself. thank you for sharing.

 

Something else to consider about silicone is that apart from the shore (hardness) there is two main types: Polyaddition and polycondensation.
Polycondensation is often cheeper, at least it was in the past, but it is harder to work with. It works by you having to add a very small and very presice ammount of hardener into a main part. If you can avoid this type I would suggest you do so. You can make molds with it, they do work and there is actually less problems with air bubbles (in my experience) but the hardener is very toxic and the whole thing is just hard to get right.
Polyaddition is the type where you mix two, often equal by weight, parts together It's safer and easier to work with. It used to be very expensive, but prices and availability have become a lot better over the last ten years or so. It will tend to catch more air, though, so it will increase the need for a preassure pot.

One last thing to think about when starting out, if you work without any means of degassing the silicone:
The main problem with air bubbles in the mold is not open bubbles, it's the ones under the surface. As the polyurethane gets warm during curing, the trapped air in the mold will expand, making the previously perfectly smooth casting surface knobbly. This causes pock marks in the finished piece. A harder silicone will deform less by the heat and create less marks, even with the same ammount of airbubbles trapped in it. Therefore choosing a harder silicone, and perhaps even plan your entire project to consist of smaller pieces (that develope less heat) is worth considering.
Another thing to think about is that air move uppwards, so the highest concentration of bubbles will be in the part of the mold that is up when you make it. Making a two part mold means that you can get the least amount of trapped air near the casting surfaces on both sides of your piece, while a one part mold will inevitably have more air on one side than the other.

 

@Lillith that's great technical information, thank you!

Sorta related question for those of you who use pressure pots: How big an air compressor do you use? And where did you purchase your pot/compressor?

 

Hello everyone, I'm new here, I'm currently learning how to use Smooth On's Task 9, it is amazing and it takes the pigments very easily and they look good, i've been using So Strong pigments but they're translucent and Task 9 cures in an amber color (So don't make that mistake when buying), I'm gonna get the UVO pigments and I think they'll work great.
Now, Task 9's cure time is short (about 60 minutes) but it gives you enough time to handle it, you still have to be fast though, so I'm thinking for my next test mixing the pigments to one of the parts of the resin and then just mixing enough for one of my molds and take my time with each one of them, that way the color looks good in all of the pieces and I can keep an eye on them to reduce the bubbles, I'm thinking about getting the equipment to do pressure casting cuz it still makes a few bubbles while it cures so that's kind of annoying. For my molds I used Mold Max 30, the silicone's quality is amazing but it's hard to handle since it's really sticky and the proportions are 100:10, I'm gonna try to buy Mold Star 30 for my next project. Anyway I hope it helps you guys! If you have any questions about those materials let me know and I'll try to answer them! hehe

 

This thread has inspired me to cast my head myself rather than find a casting company and end up with extra copies I probably won't be able to sell. I'll probably order the silicone this week and at least try to get the mold done before we get triple digit temperatures later this summer. I have a few questions, though.

1) Is the trial size of Sorta Clear 40 enough to create the mold for a small 1/4 head (5-6 inch)? I used the product calculator on the site, and the answer seems to be "maybe." The problem is that I don't know how much extra silicone needs to be around the head on all sides when the mold is created. I'm probably going to do a two part mold.

2) I know to work in a place with plenty of air circulation and with a respirator. However, how bad are the fumes in areas adjacent to the work space, assuming the door is shut?

 

1 - I don't know how much silicone you have on hand but you'll need to make at least an inch around your piece, to make your mold sturdy and avoiding any deforming during resin-casting. Here's how I did it:

Molde - processo by Lilian Pereira, no Flickr

2 - Silicone fumes aren't nearly as bad as resin's, so there's no need to isolate your workplace once your pieces start curing.

 

Thanks for the info

I'm looking through the Smooth-On products, and I think I might get Mold Max 14NV instead, because it supposedly doesn't require degassing. Has anyone had experience with that product?

 

@Zardi
I do not have experience with Mold Max, but I found this thread that compares properties of different kinds of Mold Max silicones: Resin Addict Forum • View topic - Mold Max 14NV 25 or 30?
I used Smooth-on OOMOO 30 and I was pretty happy with the molds I made without degassing. I had more trouble with the air bubbles in the resin itself :/ But all the parts I cast were smaller than a 1/4 head, I think there should be less trapped air bubbles because the features of your master are larger.

 

Great image. Thanks for sharing

 

Hi again! Still preparing for the casting process... So, @LilaAIP thanks for the pic! It made me nervous a little bit, cause I have prepared moulding box out of LEGO and I have left definitely less than one inch space left to the walls I have no more LEGOs for expanding it. And the other reason is that the consumption of silicone (and the cost of it) will be huge! So I can't imagine adding more material... that would mean no more will be left for the head's cap. The only comfort is that I have silicone hard enough to withstand, I hope.

Meanwhile, I need help with the resin pigmentation. I have mixed the toners - without adding white, as the resin is off-white itself. So these are the strong pigments (other brand than So-strong, EU ones). Do any of you have an idea, how much of the toner should I admix to the resin to obtain flesh tone? For example, if I use 100 g of resin for the head cast, would 1 g of toner be enough, too much or too little for a medium (let's say peach) skin tone? I have no clue

 

I ended up buying Mold Max 14NV and some mold release It's still sitting in a box at the moment, but I hope to try making a mold next weekend if it isn't still raining.

I'm looking into resins, and I've realized that pot time and working time are not actually the same thing. I don't see where Smooth-On lists the working time of its resins, just curing time and pot time. How can you tell how long you've got to actually pour the resin?



Edited for a typo that was bugging me.

 

@Zardi
Pot life is the time while the resin is still workable, liquid. Curing time is the time needed for resin to fully harden, after which it can be taken out of the mold.
Smooth-on apparently has a page for terminology too: Definitions of Technical Terms

 

Oh...so then pot life and working time are the same? Darn conflicting sources In that case, it seems like it would be easier to have a longer pot life. I'll probably look into Smooth-Cast 327 in that case, along with UVO colorants and Sun Devil UV protection.


I saw this on Smooth-On's product descriptions:

I've seen a couple of BJD casting tutorials on YouTube, and they seem to put the pouring spout at the top or bottom of the head, along the circumference. But if you're supposed to pour the mixture into the lowest point of the containment field, then that seems to imply that you should place the piece upside down when making the mold (for example, laying the headcap down so it looks like a bowl) and having the pouring spout right into the middle, so the resin pours directly into the bottom of the "bowl" and then works its way up the mold as you pour in more resin. But that seems like it produce huge air pockets, unless you poke more holes along the top of the mold to let the air come out. Am I misinterpreting something here?

 

Yep, that's pretty much how it is. You can either cut out more air openings after the silicon has cured or make them before pouring silicon, using straws or toothpicks. And don't forget to tap your molds immediately after pouring resin, so the air bubbles can work their way out.

 

Ok, that is useful info! In that case, I think the system I'd constructed to attach the headcap to the head may be too complicated to make a nice mold for, at least for my first go (there is a post on the headcap, and a corresponding hole on the head). I might as well convert it to a magnet system.

 

A full inch sounds like a lot, but that will depend on the hardness of the silicone, the size on the mold and to some degre the complexity of the part you are casting.
I would suggest casting the head-cap before the face, as it's usually a smaller and simpler piece with less places that can trap air and the tolerance for casting flaws is usually a bit bigger. Over all just an easier thing to get right.
Also, if you have never cast anything before, consider doing a few smal material tests to get used to the materials without risking a lot. You can work out the pigment ratio at the same time.
Legos work fine, but you may need to seal the inside with something to keep the silicone from seeping into the pieces and cause a lot of material waste. I have had great success with vaseline+talcum powder, but some silicones don't like that, for those I use polyvinylalcohol. You can read up on the materials you use for clues of good methods, but you still need to test these materials out yourself to see what works for your combination of materials and conditions.

I likely use different pigments than you, but this is how I do it:
I mix the color I want from primary colored pigments and for soft tones I mix them into opak white pigment. I make the color a little bit more saturated than I want the finished piece, but not a lot. If I need a lot of parts to be the same color I mix a larger batch of pigments and keep the rest for the future.
The I prepare the molds and I refer to my notes from previous tests and casts to see how much resin I need.
The polyurethane resin I use comes in two parts, one white and one clear. I usually mix my pigments into the white part, because the result will be pretty much what the finished color will be, so it gives me one last chase to correct it if something is wrong. Again, if I need to cast a lot in the same color, I mix a large batch of pigmented resin. That way I know the pigmentation will be the same throughout the casting batch.
Then I measure out the amount needed for the prepared mold out of both parts of the resin, mix it and pour it.

 

I am almost done creating the mold for my head (just have to pour the "inside" of the face, then cut the pouring spout and vents). I'm ordering Smooth-Cast 326 along with UVO pigments and Sun Devil. I chose 326 so I won't be quite so rushed with the short pot life that 325 has. Hopefully I'm not making a mistake by not going with 327, which has a longer pot life. I do not have a pressure pot or vacuum chamber, and would prefer not getting them.

I've been watching a few casting videos on YouTube, and came across this one:

I'm wondering if a modified version of this technique could help avoid bubbles on the facial features of a doll's head? My 2-part molds are "outside" and "inside" the head, so I wouldn't let the resin partially cure and then join halves. Instead, I'm thinking of initially leaving the mold open and pouring a bit of resin into the face (picture it lying face down like a bowl), then working the resin into the facial features like this guy does in the video, and then carefully placing the "inside" half of the mold into place and pouring in the rest of the resin. Smooth-Cast 326 has a 9 minute pot life, so it seems like there would be enough time to do that.

I'm not going to sell these castings, so it doesn't bother me if there are some bubbles on the inside or in areas hidden by a wig, I just really want to avoid them on the face. Has anyone tried doing it this way, and did it work? How much do you think this would help compared to dusting the mold with baby powder first?

 

The main problem in using this technique on a head mold would be the resin running and pooling on the lowest parts of your mold. Maybe if you combine this with technique with rotocasting/slush casting?. Here's an example on how it works:

 

Ok, I'll check out that video. Thanks