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What urythane or poly resin is best

Nov 30, 2011

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    1. I have been trying to wrap my mind around it for some time. I have done some casting in polyurethane resin and generally liked how it behaved, but did not like it's general quality. I'll explain:
      First off its natural color was a pale tan and I want white. All the dolls that I have ordered are white and I want the ability to cast mine in white. I can always pigment the resin if I want it to be tan, but I can't make a tan resin white.
      Next it felt like plastic unless I added something to it like porcelain dust or marble dust. I didn't like the weight of it. I know it's plastic, but the dolls that I have ordered have this feel to them. they feel more natural. Now on my sculpt it was not shiny or plasticy in appearance, but it just felt light and warm like plastic.
      Is there a specific resin that some would recommend to cast in? I am about to start making heads and I need something really good as I am really past the junk mold stage of it and junk cast. I have two heads right behind me which acted in that manner for me and I want to move on to making something I can really be proud of and would accept as being saleable.
      I guess I am looking for what is most commonly used, very specifically, to cast quality doll parts. I want to find something that I will be happy with. Right now I'm using a polytec resin that has a five minute set time, but it cures a pale ivory tan like I mentioned. The two minute cures white but I was afraid it would set so quickly I wouldn't be able to get it to behave. Honestly the five minute stuff I have is really loose for about 10 or 15 minutes. Is the 2 minute stuff the answer? I need the exact type of resin, set time, and what qualities I need to look for so I can find something in the US that is the same as what they are using in China, Japan, and Korea. I know what I have is like the smooth-on stuff and I have the UV agent to add so that the resin doesn't yellow as much, even when left untreated with MSC. I'm frustrated because I don't trust the materials available without some feedback and I only have a small amount of funds to invest in my production models. I would love any feedback that anyone has.
       
      #1 Myrretah, Nov 30, 2011
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    2. I am no expert on resin and have been using Smooth-Cast 300 for a short while now. Since I don't have a pressure pot, I went with a casting kit that included this urethane resin. In the future I plan to use Smooth-Cast 305 with a longer pot when I use a pressure pot. But the kit I got helped me learn about silicone mold making and urethane resin casting. Also keep in mind that some of what you are asking about will be different in opinion from one person to another.

      White Well, Smooth-Cast 300 is white.. ish. When I look at my castings it is white to me, but when compared to white paper you can see that it is a bit off white. How white are you expecting it to be? I haven't tried adding color yet either.

      Feel Some of the feel you get from your casting can depend on the original sculpt that was used to make the mold since the texture will transfer. A slick shiny surface will have a different feel than one that was matte or textured. My castings that are matte feel smooth and silky to me. Not too cold to the touch or too warm. Doesn't really feel plastic like to me... well compared to a rubbermaid container...haha But a shiny casting (leftovers in the mixing cup) feels more plastic like to me. Definitely not a feel I want for my doll. I can't compare it to marble or porcelain though since I can't recall the feel of either.

      Weight Hm, I don't have any other resin or dolls to make a comparison. Some of the weight will depend on how thick you cast your parts, how you made your molds, and your sculpt design. I have not yet completed a doll in my resin, so no real comparison from me can be made.

      Pot Life Smooth-Cast 300 has a 3 minute pot life. The instructions say to mix for 90 seconds. I prefer to measure out both portions separately then mix together. Then I pour it back into the other cup and mix again. Then maybe pour it back into the other cup and mix some more. Carefully so I don't add more bubbles, but quickly enough that I am not wasting precious mixing time. By the time 60 seconds have passed I fill my syringe and pour into my molds. I have to say, there isn't a whole lot of time to think idly while you do this. Filling 2 small head molds is all I have time for. The Smooth-Cast 305 has a 7 minute pot life, which I plan to use when I get my pressure pot since I will need that extra time.

      UV I haven't added anything to the resin for UV. I did put some resin outside where the sun hits occasionally to test how it yellows. I haven't checked on the piece yet. I plan later to do a more controlled test on yellowing.

      For now I am pleased with Smooth-Cast 300, but that is not to say there aren't better out there. I wish I can try many different types of resins to see the difference, but that can be costly. Just like I would also like to try various types of silicone rubber... but again costly. Hopefully more experienced casters will jump in with what resin they use and more information.
       
      #2 Mothi, Nov 30, 2011
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    3. Yeah, the stuff I have now just feels light. That's the best way that I can put it. the surface doesn't feel like plastic when you run your fingers across it or anything like that because I was so twitchy about how the surface of my sculpt was. I think I burnished it down with an agate burnisher that I use on silver, then very carefully treated the surface afterward so it was uniformly matte and even, but I can't get over the weight issue. It feels like a garage kit, like a cheap recast because of the weight (I own a few of those) and the doll I have (A resin soul gang) has a completely different weight to the resin and feel, even on the interior hollow areas where he wasn't sanded. Twigling mentioned that it may be because I was just pouring it and not using a pressure pot which would up the density as it would get rid of any foamy little bubbles that were there at all. I may have to get Smooth On. That's what she used too. I was hoping to stick with polytec resins but it is more important to me to get the right stuff exactly. I have noticed that the polytec five minute stuff is still REALLY runny for up to 15 minutes even though it says its pot time is 5. It may be more worthwhile for me to move over to smooth on anyway if their numbers are more accurate. I made a mother shell for a glove mold outta what I have and it was a serious pain in the rump because of how long it stayed gooey. It kept running away and I was there for about 30 minutes just to get it to stay on the high point of the silicone sleeve. 30 minutes and it still had the consistency of thick all purpose glue! Man that was insufferable. Thank you for your input Mothi. As I experiment with the UV stuff I will let you know how it behaves itself and what it does for interaction with the resin I end up with.
       
      #3 Myrretah, Dec 1, 2011
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    4. SC305 is bright white and has a 7 minute pot life (you can get a faster and slower set as well). It will yellow over time but you can ameliorate this by adding Sun Devil UV protection, which is another SmoothOn product. Btw, I always mix my resin by weight because it's more accurate. As for the plasticity, you will have to test it out to see how you feel. I have tried some of Polytek's stuff, and didn't like it, either too fast setting or too flexible when cured, and not the right colour. Smooth On seems to have much more option in their range of products.

      Task 2/3 is harder and denser that 305 but also more viscous, therefore harder to pour into a mold and avoid air pockets and bubbles forming. When mixed properly, it does cure bright white and slightly translucent though.

      Exposing the resin to heat might speed up the curing time. Likewise I have had partial success putting some fast-curing resins in the fridge (double bagged) overnight to make it possible to work with.

      I am told that Polytek is an offshoot of SmoothOn, someone from SO left and started their own company after stealing recipes from the mother company. However I'd maintain that the products and customer service from SO is superior, although technically I only ever dealt with an Australian retailer of Polytek products, so maybe that was part of the problem.
       
      #4 twigling, Dec 1, 2011
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    5. Although the Smooth-Cast 300 has a 10 minute cure time, I find it is better to let it cure 30 minutes before removing. It could be because of the temperature the mold/resin was kept at during the curing process, but you can unmold it at 10 minutes. It is just not as solid as I like it until after 30 minutes... a bit flexible at 10 minutes. Your mileage my vary.

      As for the weight of the resin. Would it help to look up the technical information of the resin you are considering and look for what is stated for the Specific Volume. It is listed as x number of cubic inches per pound. (cu.in/lb.) Smooth-Cast 300 is 26.4 cu.in/lb. And when you do some lovely math, it comes out to be 0.6 oz per cu.in. You could use the technical data to help give you an idea how much weight difference various resins have.

      You could probably find out how much volume your casting has and figure out (using the technical information) how much said casting should weigh and compare it to what it does weigh. You can then see if the weight of the casting is close to what is estimated or if it is lighter because it has a lot of bubbles. But of course that is getting a bit complicated with math and is rather technical if you aren't into that kind of thing. I can be a bit of a freak about it so I am just mentioning it in passing. But the small head I cast from SC-300 feels to be a good weight. There is substance to the casting. No idea how else to explain it.

      Sorry if I made your brain hurt.
       
      #5 Mothi, Dec 1, 2011
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    6. AAAAh! too much math first thing in the morning!!!! Just kidding. That is a good way to tell though, because I can compare the weights of the parts that I have to that of the doll I am making and get an idea of what they should weigh when compared to my parts with the resin I am using (I hope you followed that). that way I can see if I am on target for the general weight in hand. My fear was that, I only have one doll and I could tell the feel by weight was different between the resin I have, and the resin my doll is made from... so if I were to sell it to someone who has 10 dolls or 20 dolls, or maybe just a few they love, they would notice as well when they go from one of those, to playing with mine. My intention is to cast in both resin and cold cast porcelain (which would naturally be heavier) with a lot of my sculpts so it is important to me to find a quality product to work with as I will already have SO much trouble shooting.

      I knew that polytec was an off-shoot of smooth on. It's hilarious because they say that they left because they thought they could make a better product than smooth on and felt limited by the company constraints, which is why I had mild trepidation about ordering from smooth on to start with. You wouldn't think there would be so much drama in the resin business, but I guess there is simply drama in any business. I may still order my silicone and mold making stuff from polytec as I have had pretty good luck there, but really I need the materials that smooth on offers as far as the actual resin goes and will invest properly once I get my pressure pot :)

      I'm up the coast from you Mothi and suffer from giant leaps between horrible humidity to it being so dry my hair is static clinged to my face. I would be very interested in any advice you have on how to get things to behave themselves. My experience in the dental lab has made me a pretty fast pour with minimal gaps or bubbles in the surface, so my largest concern with set up is that I have enough time to mix it properly and then get it into the mold as I tend to take my sweet time making sure it is all mixed right. I have only made about ten batches with the creamy stuff I have so it could be simple lack of experience on my part which I will grow out of.

      Twigling I am in love with your Zen. I set it up on my tablet so that I can bring it all over with me. I am fascinated by your process and your journey. Thank you so much for making that available! I mix my resin by weight as well. It is so expensive to also have concerns about having wrecked a batch because I went "on the fly" with it. I have a lovely old scale that I have taken to using at my friend's studio (It is set up in grams and has these little bitty weights... I think he got it from a pharmacy that went out of business). It isn't digital, but because of this I don't have to worry about gumming it up and can clean the stainless steal fittings off with whatever I need if I spill (I haven't spilled but he sent a glass full of part b over on its side and I just about went out of my skin over it).

      I have been reading the "bubbles" thread on here as well and hope I can use both of your advise, and advise from that thread in the next few attempts I have. I'm probably going to use the resin I have left for mothershells as I don't like it and just get some smooth on to try in the bright white like you both suggested. It is important to me to get it right!
       
      #6 Myrretah, Dec 2, 2011
      Last edited by a moderator: Dec 2, 2011
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