7 Reasons Your Epoxy Resin Is Yellowing [And How To Fix it]
Working with epoxy resins is quite an extensive medium for art forms due to the versatility of its use. With your epoxy resins, you can make resin coasters, keychains, resin jewelry, geode resin art, cutting boards, serving trays, river tables and resin tables, and much more.
One very important thing you need to know though, is that all resin will yellow over time. Don't worry, we have ways to prevent this from happening quickly and the degree to which it will happen. There is a lot you can do.
Yellowing Resin Is A Common Occurrence
Sometimes you might notice that a beautiful cured epoxy resin piece that you created is now turning yellow. This can happen months or years after pouring the resin. You might also notice that the resin has a yellow discoloration inside the bottles even though you have not mixed the hardener and resin together yet.
We are going to discuss why this happens and why the resin has a yellowing discoloration.
Yellowing epoxy resin is definitely a concern. Especially if you have white faux marble countertops that have been poured with resin, or a high end geode resin art piece that is mostly white. Since resin is fairly expensive, it's a shame that it is prone to yellowing.
Unfortunately, most companies don't tell people that their resin can yellow. It can be an expensive lesson, especially if you are in the resin business and selling your handmade resin creations, resin countertops or resin art pieces and jewelry.
Epoxy resin turns yellow due to several reasons. The resin may have heated up too quickly when curing or there may have been a reaction to the colorant that was added. Poor quality resin will turn yellow within a few months, especially when there is UV exposure.
UV light and light exposure are your biggest enemies when it comes to getting a yellow hue in your clear resin.
Why Your Resin Is Turning Yellow
1. Poor quality epoxy resin will yellow more quickly
Choose an epoxy resin that has a good reputation of not yellowing. These companies will usually spend more on their formulation by adding a UV protectant in the form of UV and HALS stabilizers.
This is why a good quality resin may be more expensive, but it is 100% worth it if it will make your pieces last much longer. Many resins have stabilizers in them to help minimalize this color shift, but not all forms of epoxy resin products are created equally.
What are UV light stabilizers?
According to a paper called The Selection of Polymeric Materials on Science direct, "UV stabilizers protect the polymer from the degradative attack of UV energy, or exposure to fluorescent light and filtered daylight".
What are HALS stabilizers?
According to the Plastics Technology in the polymer database, this is what HALS stabilizers are:
One of the most important classes of antioxidant for long-term heat protection of polymers are the so called hindered amine light stabilizer (HALS) which are very effective inhibitors against free radical induced degradation of polymers at low and medium temperatures.
Brands of epoxy resin with added UV light protection:
- ArtResin (UV light stabilizers and HALS stabilizers)
- Resin Obsession (UV light stabilizers added)
- Craft Resin (UV light stabilized formula)
- Let's Resin (UV light stabilized formula)
2. Resin that has exposure to UV light will yellow faster
Try to keep your cured resin from UV light exposure in the form of direct sunlight. If you are selling art pieces or jewelry, include an insert letting your customer know to keep their pieces out of the sun. Resin that is constantly exposed to sunlight is prone to yellowing more quickly.
Once there is exposure to UV light and the UV light hits your resin art, it starts to break it down. And if it is regularly exposed with excessive amounts of ultraviolet waves, then you can expect your resin art to change color or there will at least be observable discoloration.
Whether you have a synthetic resin, a UV resin, a polyester or an epoxy resin, the most common reason for resin yellowing is ultraviolet light.
3. Adding colorants that are not compatible with the brand of resin may cause yellowing
Sometimes it's the colorants that are causing the epoxy resin to yellow. Also, if the brand you are using comes with their own powder colorants it might be best to use their in house products that are specially formulated to work with their products.
Companies such as ArtResin and Let's Resin have their own colorant brands that work very well with their resin, plus they come available in large bottles which will help prevent yellowing.
There are some tried and true colorants that will work with pretty much any resin which is discussed below in the 'how to fix yellowing resin' section.
It is also good to know that titanium dioxide, which is a white powder, can cause a reaction with the resin and cause it to yellow more quickly.
4. Resin that heats up too much when curing or mixing can cause it to yellow
There are certain resins that are specifically formulated for deep pours. If you are wanting to pour anything deep, like a table or deep section for a river insert, then be sure to check that the resin you choose is made for that and made for deep casting. There are deep casting resins for home use as well as for industrial use.
Using a regular resin for a deep cast may cause the resin to heat up to the point of melting your form. That will most likely cause yellowing, among other problems like an imperfect cure. So be sure to do your research about what types of resin to use for deep pours.
5. Misuse of a heat gun can cause burning and yellowing of the resin
Many artists and resin creators like to use a heat gun to move the resin around and help those microbubbles escape. This is especially popular for making lacing effects and for geode resin art.
Using a heat gun is totally great for getting bubbles out of resin and moving color around, but make sure you are not burning the resin. Some heat guns are very powerful and should not be used to move resin around.
Buying a heat gun for resin with a controllable temperature is best, even if you only have high and low options. That way, you can start on the lower temperature setting and see if that works with the resin brand you are using.
A heat gun should never be kept on the same spot for more than a few seconds; it should be used in a circular motion over your resin to move it around and eliminate bubbles. And never hold it over your silicone mold too long.
*If choosing between a heat gun for epoxy and a torch, we always recommend going with a heat gun with a variable temperature setting so as not to burn your resin or mold with the high temperatures of a flame.
Read our article about choosing the best heat gun for resin
6. Keeping cured resin pieces outside may cause yellowing
For those who are pouring a resin table or ornament to keep outside, it might turn yellow within just a few months. The sun can degrade the polymers and cause yellowing.
This is why it is important to know what you are going to be making with your resin so you can buy an appropriate resin with UV light protectants in it. There are also proper UV light protectant sprays that you can finish your resin art with, and we will cover that in the solutions below.
7. Hardener that is exposed to air will yellow inside the bottle
It happens all the time. You put your epoxy resin supplies away and then months later want to make something and notice the hardener has turned yellow in the bottle. This is because the hardener has been exposed to the air and it's starting to oxidize.
You can still use the hardener. When it is mixed with the resin and poured onto a surface or mixed with colorants it will be less yellow looking.
How To Prevent Resin From Yellowing
Once the cured resin has turned yellow or starting to yellow on the sides, there is no way to reverse it. The epoxy resin will continue to get even more yellow over time.
1. Only purchase high quality resin
Resin can be expensive but when you purchase resin that is not of good quality, you are pretty much going to get yellowing after even a few months.
If you are using a cheaper brand of resin and want to use colorants to make it a dark color or don't care if it yellows over time, then by all means save the money and go for something less expensive. Otherwise purchase resin from a company that has good reviews about yellowing.
If you are looking for a high quality multi-purpose resin that has good UV light protection in their formula, we often recommend ArtResin. They make a good quality resin that is good for coasters, tumblers, jewelry and coating pours.
2. Purchase quality colorants that are made for resin
Sometimes it might be as simple as using the right colorants. Powders are generally better than a colorant that has too much liquid in it. Also, it's generally best to use colorants and resin from the same brand.
Chameleon Colors have some of the best color options that are high pigmented and made especially for resin. They offer holographic color and pretty much any color you need. A little goes a very long way.
3. Store the unused resin and hardener in a cool, dark place
Once you have opened the bottles of resin, pour the desired amount of resin and hardener, and then make sure the caps are put tightly back onto the bottle quickly. Get the resin and hardener out of the light and back into a dark place to prevent a change of color. Most forms of resin and epoxy hardeners will change color right in the bottles if improperly stored or they are there beyond their shelf life.
4. Pour another layer of colored resin to hide the yellow color
If you are updating countertops or an art piece that is starting to yellow this is the best way. Or, unfortunately you might just have to live with the yellow color.
5. For smaller pieces you can try to sand off the yellow color
Be aware that it might be too late for this. The yellowing might have gone through the whole piece. Examine it carefully to see if it is actually worth it.
6. Keep to darker, cooler colors when choosing a color scheme
Darker colors like purples and blacks seem to hold up a lot better than lighter colors. And now that you know the resin could possibly yellow, choose colors that will go with the yellow color. Not ideal, but a good tip to know if you have resin to use up. You might even want to choose a yellow or gold color scheme to start out with.
7. Use a resin that has a UV stabilizer in it
We can't stress this point enough. Do keep in mind that UV stabilizers may keep the resin from turning yellow more slowly. But they will not completely prevent the epoxy resin turning yellow, especially after many years.
Every resin will yellow slightly over time, some take longer than others to yellow, some don't yellow as much as others. Look for a resin that already has a UV light stabilizer in the formula.
8. Keep a resin yellowing chart
If you are planning on working with resin over a long period of time, then start to keep a chart. Whenever you pour the resin, also pour a small sample and keep notes with the date you poured it.
Eventually you will have a good collection of resin pours to go back on to see what's happening and what might be the cause of the yellowing or the resin turning a different color. As as you use new products, you will be able to note their natural process of yellowing over time, how much it yellows in a controlled environment, and if it will stay clear.
You can even make two samples and keep one in a controlled space (dark, cool room) and one in a place where it would normally be kept, for example, in a living room, so see the natural effect. Then you can compare the yellowing process with exposure to UV light.
*Be sure to share your results with us if you are interested in doing this! We would love to hear your story! We have a comment section below this article. This would be a great study to do if you plan on doing epoxy flooring anytime over the next year or so, or it may help you find that perfect epoxy for a clear coating on your art.
9. Seal your resin with a UV protectant spray
You can seal your resin with a UV protectant spray once it has gone through the full cure and is no longer off-gassing.
UV sprays work with synthetic resin, UV resin, polyester resin and epoxy. Just a thin layer will do as long as your resin is dry (and can cure properly). You do not want to spray this while your resin is still in a liquid state.
Here is one many resin artists use:
Here are some more resources you may be interested in:
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USE RESIN SAFELY
No matter what type of resin you decide to use, always use personal protective equipment (PPE). Take time to carefully go over safety data sheets before making anything with resin, and make sure you have the proper gloves on (not latex) and the right respirator for resin protection.
And please remember, even if your epoxy resin of choice is "VOC-free, odor free" and/or "non toxic", please always wear the proper respirator for epoxy resin.
Here is the BEST respirator mask for epoxy resin: this Full Face Organic Vapor Respirator checks off all of the boxes for resin safety, and comes with
- free 30 day returns
- a 1 year factory warranty
- free US shipping and free shipping on international orders
Here it is:
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