Epoxy resin is regularly used in art projects. But do you know what it is or why artists use it?
Well, first let’s take a step back and examine the basics of epoxy resins. Epoxy resins are often used as construction materials, but they’re also sometimes used in art projects.
Epoxy resins are made up of two different parts: an epoxide group (which is often referred to as an oxirane ring) and a resin that has multiple hydroxyl groups.
Does epoxy resin yellow in the sun?
The answer is yes. Epoxy resin can yellow in the sun. Regular, commercial resins are designed for indoor use and for that reason do not contain any UV stabilizers. UV light (sunlight) will cause an exothermic reaction on the surface of your resin, which can lead to a yellowing effect over time.
You can avoid this however by using a UV-resistant epoxy resin, to begin with. Some suppliers offer epoxy resin formulas that use special additives to prevent sun damage and discoloration.
These types of resins aren’t cheap, however – they tend to cost at least twice as much as regular resins.
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How do you keep epoxy from turning yellow?
- Keep it out of direct sunlight
If you are working on a project that will have prolonged exposure to sunlight, there are a few ways to keep your epoxy from discoloring.
- Minimize UV exposure
This is the easiest way to keep your resin from yellowing and does not require any extra work or supplies, just a little planning. Avoid using clerestory windows and glass doors if possible, or put up curtains or blinds to block the sun.
If you are working with an outdoor project like an epoxy river table, try adding a removable top or covering that can be used when you aren’t enjoying it as much.
This will also protect your table top from rain, dust, and other elements that can damage it!
How long does it take for epoxy to yellow in the sun?
People often ask me how long it takes for epoxy resin to yellow in the sun. The short answer is: “it depends.” That’s a pretty unsatisfying answer, though, so let me elaborate!
For starters, not all epoxies are created equally. Low-quality resins with poor UV stability will yellow faster than high-quality resins with excellent UV stability.
So the first thing to consider when determining how fast your resin might yellow is the quality of the product you’re using and its overall UV stability.
When looking at quality, there are actually two things to consider: how well the product was made and what ingredients were included in its formulation. Let’s talk about each of these in turn…
What happens to epoxy resin in the sun?
Does epoxy resin yellow in the sun? Yes, it can! When exposed to UV rays and heat, epoxy resin can turn cloudy, white or yellow. It can also get soft and sticky—and in some cases, even warp, bubble, and crack.
Epoxy is especially sensitive to sunlight during its curing process. If your casting is still curing when it’s exposed to sunlight (which contains UV rays), your piece may cure with a hazy yellow or cloud-white color.
Even if the piece isn’t cured all the way through yet when you expose it to sunlight, any layer that has cured will appear hazy or cloudy due to exposure to UV light before curing was complete (see photo above).
However, even after your casting is completely cured (hardened all the way through) but then exposed to sunlight for a long period of time, you might notice that over time your casting becomes more dull or opaque—especially if it is a color like blue that’s particularly susceptible to sun damage.
This discoloration happens because of oxidation occurring at the resin surface as a result of exposure to oxygen molecules in the air combined with UV radiation from sun exposure.
Why has my resin gone yellow?
Polymerization is a process that transforms something into plastic. During this process, the epoxy resin gains heat and energy. As the resin cures, this energy causes a chemical reaction with carbon atoms called double bonds. The double bond produces oxygen molecules (O2).
This O2 then reacts with other molecules in the epoxy and turns it yellow.
Ultra Violet rays
Even if your resin piece is indoors, there will be inevitable sun exposure over time. Ultraviolet rays from sunlight can cause color changes to epoxy resin over time, even if it is sealed with a UV protectant finish.
Pigments & Dyes
Different pigments and dyes vary in their ability to resist discoloration due to UV light exposure. It’s important to look for pigment manufacturers that support resistance against fading or discoloration due to UV light exposure when possible.
How do you fix yellow resin?
The first step to fixing yellow resin is understanding why it’s happening. Epoxy resin can turn yellow if it’s exposed to UV rays. This is called UV degradation, and while this process is inevitable, there are some steps you can take to fix your yellowed epoxy resin.
You can sand off the top layer of the discolored epoxy resin, then use a polishing powder or other finishing compound to restore its shine.
You could also add in a UV blocker additive that will protect your work from further discoloration, but unfortunately, these additives tend to turn every piece of artwork you make into a permanent nightlight (i.e., your artwork will glow in the dark).
Can you fix yellowed epoxy?
Once you’ve confirmed that your epoxy has indeed yellowed, it’s time to figure out how to fix it. First off, is the epoxy yellowing limited to one area or all over? If there are only a few spots here and there, the most likely cause is something that contaminated those areas.
If this is the case, you can fix the problem by sanding down those particular areas.
If your epoxy resin has yellowed all over, however, then you’re dealing with a different issue. Before going through the entire process of sanding down your piece and re-coating it in an attempt to restore its original color (which will probably result in needing several more coats because of something called “dissolved air” which we won’t get into right now), try using a UV filter mixed in with your next batch of resin before pouring it on.
You might also want to consider coating your piece with polyurethane after applying a new layer of resin (I do this personally). Polyurethane acts as another layer of protection against UV rays.
However noble these attempts may be at preventing further yellowing from occurring after fixing the problem, unfortunately, I don’t have any guarantees for you other than this: if your epoxy does end up turning yellow again after using those methods, then you’ll need to repeat this whole sand-it-down-reapply-a-coat process all over again!
What epoxy does not yellow?
There are many different brands and types of epoxy on the market and each is made with a different formula. So, just because one epoxy resin yellows, does not mean that all will.
The way it works is that there are additives to epoxy resin that prevent it from yellowing in UV light.
These additives work in a few ways: they absorb, scatter or reflect the UV rays. In order to ensure your epoxy resin doesn’t yellow, it must have some sort of UV protection added to it by the manufacturer.
When you’re looking for an epoxy resin look for a product that has any of these words in its description:
- UV resistant
- UV stabilized
- UV inhibited
- UV protected
- UV protection
Conclusion
As you can see, epoxy resins do yellow in the sun and the sun will eventually yellow epoxy resins. You can keep epoxy from turning yellow by covering it and keeping it out of direct sunlight. Epoxy resin may yellow in the sun after a few months and some resins yellow more than others.
