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Clear resin turning yellow

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Hi all,

I am hoping to learn if you've experienced this problem and have any tips to fix it: I have a replacement canopy set made of clear resin made for the Revell/Monogram 1/48 P-61. I bought it about 5 yrs ago and just now getting to the point of using it. 


Problem is, the parts have developed a yellow discoloration. The thicker sections of resin (such as the resin pour stubs) are clearly more yellow and even somewhat opaque than the thinner sections. The canopy parts themselves are colorless/transparent (not opaque) EXCEPT when the edges are viewed on end. When looking at the edge on end, it is clearly yellow (like a fiber optic light effect).


My questions:

1) Is this a common occurrence with clear resin? I have read on the Interwebs that some, but not all, resin turns yellow. What is your experience?

2) Can I expect the thin, clear canopy sections to eventually turn yellow and/or opaque as well?

3) Is there a way to reverse this? Maybe let the parts sit under direct sunlight (like with yellowed decals)?

4) Do vac form canopies turn yellow too?

Sorry for the many questions.





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To answer your questions:
1. Yes
2. Yes
3. Don't know, depends on the formulation of the resin. Try sun bleaching and/or hydrogen peroxide bath. Probably only temporary though, as the yellowing is a chemical reaction.
4. Older eastern European vac canopies are legendary for yellowing. But not the NZ-made Falcon/Squadron canopies, which are still clear after many years as they are made from PET-G plastic.  

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I suggest dropping by and ask the question on Garage Kit modelling forums or your favorite social media website, for what I know all the resin do tend to yellow, if they are exposed to UV light you should try to add a thin UV protective coat on it, otherwise put UV screen on your detolf



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Hi jrbm,


Here is a link to my thread on casting clear resin canopies   Link


You may want to read the whole thread, as my first or second efforts didn't turn out as well as I would have liked, but the third one did really great.  There is a discussion and some great research by a fellow modeler about which resins are least likely to yellow -- well worth your perusal!  These are some other great tips there also, about curing your silicone mold and preheating the clear casting resin before mixing, which aids in casting thin parts, like canopies!







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Most high quality clear casting resins are very touchy.  They are easily inhibited (fail to cure), most often by Tin Cure silicones (the most common).  You need to use Platinum Cure silicone for the mold.  The problem there is that Platinum cure silicone is pricey...and itself is easily inhibited by anything that even touches tin cure silicone.  So you need to very carefully segregate everything you use in mold making...tools, mixing containers, etc.  In fact, if you plan to make some platinum cure molds I would buy brand new mixing containers and spatulas and keep them separated from your other "normal" containers and tools.


I'm a fan of Silicones, Inc. RTV products and Smooth-On casting resin.  Smooth-On has a Crystal Clear line of urethane resins that work very well and are UV resistant (won't yellow).

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