Why Epoxy Resin Turns Yellow And How To Prevent It?

If you’ve used epoxy resin as a floor coating in the past, you have most likely encountered discolouration. More specifically, you’ve probably seen epoxy flooring turning yellowish over time. This process is also called ambering.

There are several reasons this process takes place. Although this is not necessarily a sign of degradation or product inferiority, it’s important to understand why it is happening and how it can potentially be prevented or slowed down.

If you’ve been working with epoxy resin for any time, you’ve probably noticed that it tends to go yellow after a while. Sometimes, this isn’t a problem, but there are projects where you might want to avoid this. So, let’s see why it happens and what can be done about it.

This is why epoxy turns yellow: your epoxy resin has been exposed to any or all of the following – UV light, high temperatures, and excessive amounts of water. Unfortunately, there’s not much you can do about this after the fact, but it is possible to reduce or hinder the impact of yellowing if you take the appropriate measures.

Reasons Your Epoxy Resin Is Yellowing

Here is why your resin is turning a yellow colour. Sometimes you might notice that a beautiful resin pour you created is now turning yellow.

This can happen months or years after pouring the resin. You might also notice that the resin is turning yellow inside the bottles even though you have not mixed the hardener and resin yet. We are going to discuss why this happens and why the resin is turning yellow.

Yellowing epoxy resin is a concern. Especially if you have white, faux marble countertops 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 resin creations, resin countertops or resin art pieces and jewellery.

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 colourant that was added. The poor quality resin will turn yellow within a few months, especially when it is exposed to UV light.

The Effects Of UV Light On Epoxy Resin

If you aren’t using ArtResin epoxy resin, your work is in real danger of discolouration from the natural environment. UV light is to blame for changes to cured epoxy resin over time. When UV light hits the resin directly or indirectly, it degrades the polymers. Although this degradation from UV light is a natural process (UV light is typically always harmful to everything on earth over time), it causes observable, undesirable, aesthetically displeasing characteristics, such as:

• gloss loss
• delamination
• cracking
• chalking
• YELLOWING

A UV stabilising agent can be added to epoxy resin formulas to mitigate these effects. UV stabilisers are very effective at preventing gloss loss, delamination, cracking and chalking, but they merely delay discolouration. In other words, yellowing is still inevitable with a UV stabiliser alone.

Yellowing first presents a light tone all over, then progressively darkens until it reaches a dark brownish-yellow hue. Yellowing will be accelerated with exposure to UV light. A resigned piece placed outside will generally reach its dark brown-yellow colour within 24 hours.

Artwork that is kept indoors would begin to discolour generally within six months to a year if it was coated in a resin product that contained only a UV stabiliser.

If the resin does not contain a UV stabiliser at all, it will reach a dark yellowing much faster within approximately 2-3 months. Discolouration has also been demonstrated in pieces that have been kept in complete darkness.

Exposure to UV light is the most common reason for epoxy resin turning yellow. When UV light hits the cured epoxy resin, whether directly or indirectly, the natural process of degrading the polymers within is sped up; this photochemical reaction is responsible for more than just turning the epoxy resin yellowish. It also causes the coating’s loss of gloss, delamination, cracking, and chalking.

This process can happen in just a matter of months.

Try to keep the resin from being exposed to direct sunlight. For example, if you are selling art pieces or jewellery, 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.

Extreme Heat

This is less common but can happen if you leave your epoxy resin supplies somewhere that isn’t temperature controlled. The finished article is placed somewhere without a temperature-controlled environment.

Long and continuous exposure to high temperatures can also cause discolouration in epoxy resin.

Although this is probably the least likely cause of discolouration in most cases, it happens when epoxy supplies are placed in an area with consistently high temperatures. This causes the epoxy to turn yellow or even light brown.

Many artists and resin creators like to use a heat gun to move the resin around.

This is especially popular for making lacing effects and for geode resin art. Using a heat gun is ok for this, but make sure you are not burning the resin. Some heat guns are very powerful and should not be used to move resin around.

Poor Quality Epoxy Resin Will Yellow More Quickly

Choose an epoxy resin that has a good reputation for not yellowing. You will have to do some research in Facebook groups and reviews. Quite a few popular brands say their resin does not yellow, but most will over time.

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 want to pour anything deep, like a lamp base or deep section for a river table, then be sure to check that the resin you choose is made for that.

Using a standard resin may cause the resin to heat up to the point of melting your form. That will most likely cause yellowing. So be sure to do your research about what types of resin to use for deep pours.

Moisture

 This is going to occur if you’ve chosen a really insufficient storage space for the epoxy resin or if you’ve opened and closed the container with the resin many different times, allowing for atmospheric moisture to contaminate the resin or if the finished article is placed in a moist place and is regularly exposed to water.

In most cases, epoxy floor coating is resistant to water and many other liquids. However, in some cases, if an opened container of epoxy resin is placed in a location rich in atmospheric moisture or when it is regularly exposed to water, contamination can result in discolouration.

Adding Colourants That Are Not Compatible With The Brand Of Resin Will Cause Yellowing

Sometimes it’s the colourants that are causing the epoxy resin to be yellow. It is always a good idea to use powder colourants over liquid colourants. Any colourant that is suspended in a liquid may react poorly to the resin over time. Also, if the brand you are using comes with its powder colourants, it might be best to use their house colourants.

There are some tried and true colourants that will work with pretty much any resin, which is discussed below in the fixing yellowing resin section. It is also good to know that titanium dioxide, a white powder, can cause a reaction with the resin and cause it to be yellow more quickly.

Oxidation

In this case, discolouration starts with the epoxy hardener, not the epoxy resin. Oxidation turns the epoxy hardener yellowish over time. This starts to happen when the container of the hardener is opened for the first time, and the air is allowed to enter.

The degree of discolouration depends on the amount of exposure. This also means that hardeners placed in larger bottles may be more affected.

Keeping Resin Products Outside May Cause Yellowing

For those 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. The elements and rain can all contribute to yellowing resin outside.

Hardener That Is Exposed To Air Will Yellow Inside The Bottle

It happens all the time. You put your 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 oxidise.

Of course, you can still use the hardener. However, it will be less yellow looking when mixed with the resin and poured onto a surface or mixed with colourants.

How To Prevent Epoxy Resin Discoloration

The best way to prevent discolouration in epoxy resin happens in the product selection process. Some products have UV stabilisers that prevent the resin from losing its gloss, delaminating, cracking, and chalking. However, UV stabilisers only slow the process of discolouration. They do not completely stop it.

Some products also have Hindered Amine Light Stabiliser or HALS. This is an additive whose sole purpose is to prevent the yellowing process. It essentially diminishes the degradation cycle in the epoxy resin that causes the discolouration.

A product that contains both a UV stabiliser and HALS will yield the best results against ambering and the other results of UV exposure.

Apart from that, making sure that your epoxy supplies have little to no exposure to moisture, heat, or air will also help in preventing the discolouration of the cured product.

If you’ve already applied the epoxy resin, you can prevent discolouration by limiting the direct or indirect exposure to UV light. Even if only one area of the flooring is exposed to sunlight, the discolouration will still spread to unexposed parts.

UV stabilisers are not enough to prevent yellowing in epoxy resin. If you are coating pieces of art-or anything creative, special and important-then you need a product that contains an additive called ‘HALS’ and a UV stabiliser.

HALS stands for Hindered Amine Light Stabiliser. Its job in the formula is solely to address yellowing. How does it do this? HALS scavenges radicals produced with UV light exposure, thus diminishing the degradation cycle that causes yellowing. 

Its protection abilities have been demonstrated time and again since it came into existence in the 1960s. A UV stabiliser is still necessary to protect against the other problems that result from UV light degradation.

However, HALS is the number one agent that works to address yellowing. So what epoxy resin product is specially formulated for creative projects?

That contains both a HALS and a UV stabiliser? that has been deemed non-toxic when used as directed and safe for home use? that is an easy 1:1 mixing ratio, and that produces a gorgeous, glossy finish? It’s ArtResin.

Use A Sealer

You can buy sealing products from epoxy resin that are designed to be “aliphatic” (that is, non-yellowing) coating for the resin. If you choose to use a sealing agent, you will need to make sure that the surface is thoroughly clean before it’s added, and you may want to roughen the surface of the resin to get the best bond between the sealer and the epoxy.

One nice additional benefit of using a sealer on your epoxy resin is that it helps to stop it from becoming stained through spills as well as preventing fading of the surface.

For Smaller Pieces, You Can Try To Sand Off The Yellow Colour 

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 worth it.

Only Purchase Quality Resin

Resin can be expensive, but when you purchase resin that is not of good quality, you will get yellowing after even a few months. If you are using a cheaper brand of resin and want to use colourants to make it a dark colour 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.

Store The Resin And Hardener In A Cool Dark Place 

Once you have opened the bottles, pour the desired amount of resin and hardener, and then make sure the caps are put tightly back onto the bottle quickly. Next, get the resin and hardener out of the light and back into a dark place.

Use A Resin That Has A Uv Stabiliser In It

Do keep in mind that UV stabilisers may keep the resin from turning yellow more slowly. But it will not completely prevent the resin from turning yellow, especially after many years. So look for a resin that already has a UV stabiliser in the formula.

 Keep A Resin Yellowing Chart 

If you are planning on working with resin over a long period of time or years, then start to keep a chart handy. Whenever you pour the resin, pour a small sample and keep notes about what you added into it and what type of resin you used. 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.

Keep The Epoxy Out Of UV Light

There are places where exposure to UV light may be minimal or non-existent. For example, a room with no windows, such as those commonly found in warehouses, where only electric lighting is used, won’t have any UV to yellow the epoxy resin with.

Purchase Quality Colourants That Are Made For Resin

Sometimes it might be as simple as using the right colourants. For example, powders are generally better than a colourant that has too much liquid in them. Also, it’s generally best to use colourants and resin from the same brand.

Chameleon Colours have some of the best colour options that are highly pigmented and made especially for resin. They offer holographic colour and pretty much any colour you need. A little goes a very long way.

Pour Another Layer Of Colored Resin To Hide The Yellow Colour 

If you are updating countertops or an art piece that is starting to yellow, this is the best way. Or, unfortunately, you might have to live with the yellow colour.

Keep To Darker Colours When Choosing A Colour Scheme

Darker colours like purples and blacks seem to hold up better than lighter ones. And now that you know the resin could be yellow, choose colours that will go with the yellow colour. Not ideal, but a good tip to know if you have resin to use up. You might even want to choose a yellow colour scheme to start with.

Why Epoxy Hardener Sometimes Changes Colour In The Bottle 

If you’ve found that your epoxy hardener has discoloured in the bottle, this is caused by oxidation, not UV light. The hardener will yellow in its liquid state more quickly once the bottle has been opened because it has been exposed directly to oxygen, and this will always be more noticeable in larger containers (just as how the ocean looks blue but a cup of water looks clear).

It can still yellow very slightly if unopened because the HDPE plastic bottles it comes packaged in do breathe a little, allowing oxidation to occur. For this reason, epoxy resins will always have a shelf life.

Once a product has begun to yellow in the bottle, it can still be used (i.e. it will still cure properly). It will always appear less yellow on a piece due to the fact it must be mixed with an equal part of the resin, thereby diluting it, and the product will be spread out in a thin layer, making any visible discolouration much less observable.

Conclusion

Now you know this is why epoxy turns yellow: your epoxy resin has been exposed to any or all of the following – UV light, high temperatures, and excessive amounts of water. However, you also know what you can do to prevent it – by using sealing agents, special formula epoxy resin, removing UV light or accepting the change and using a shade of resin that will mask it. 

FAQs Epoxy Resin Turns Yellow

Why Does Epoxy Turn Yellow?

So, let’s see why it happens and what can be done about it. This is why epoxy turns yellow: your epoxy resin has been exposed to any or all of the following – UV light, high temperatures, and excessive amounts of water. Epoxy resin turns a yellow hue due to exposure to a myriad of elements. High temperatures, excessive amounts of water, and UV light can cause the epoxy to change from clear to yellow in tint.

How Do You Protect Epoxy From Yellowing?

The best way to keep the epoxy resin from turning yellow is to prevent the reaction that causes it. Epoxies are made by mixing two chemicals together, usually a hardener and an activator or catalyst.

The chemical reaction between these materials causes epoxy to change its properties, allowing us to use them for different purposes.UV stabilisers are not enough to prevent yellowing in epoxy resin.

If you are coating pieces of art-or anything creative, special and important-then you need a product that contains an additive called ‘HALS’ and a UV stabiliser.

Does Epoxy Resin Turn Yellow With UV Light?

After exposure to UV light, epoxy resin has been shown to continue yellowing even if placed somewhere with no further exposure to light! Therefore, the easiest way to stop your epoxy from turning yellow, as we shall see in a few paragraphs, is to buy a special formula, epoxy resin, designed not to turn yellow.

Does Epoxy Resin Have A Shelf Life?

All epoxy resins and all epoxy resin hardeners have a shelf-life. The shelf life of the epoxy resin itself tends to be quite long (2-3 years), but the hardeners are more sensitive and should be used within one year.

Click to see the full answer. For this reason, epoxy resins will always have a shelf life. Once a product has begun to yellow in the bottle, it can still be used (i.e. it will still cure properly).

Why Does Resin Turn Yellow When Exposed To Light?

Exposure to UV light is the most common cause of epoxy resin going yellow, and that’s because UV is a component of natural light. UV is a mild form of radiation that can be dangerous to human health in the case of prolonged exposure, and it can cause genetic mutations and cancer.

 In the resin, the UV excites the molecules in the polymers and causes them to break down over time.

It is a natural effect of exposure to light. Therefore, yellowing begins immediately when the resin is exposed to light though it may take time to become noticeable to the eye.

Are epoxy floors a good idea?

Extremely safe – Epoxy is a very safe coating for your hard floors. It’s slip resistant, shock resistant, and less abrasive than concrete and other types of industrial flooring. It’s also water resistant, and will protect your floor from any spills, including harsh chemicals that would harm other types of floor.

What are the disadvantages of epoxy flooring?

Cons of Epoxy Flooring

• Strong Application Fumes. During the epoxy application process, wet epoxy gives off an unpleasant smell. …
• Long Curing Time. …
• Slippery When Wet. …
• Economical Flooring Choice. …
• Resistant to Damage. …
• Weather-withstanding. …
• Aesthetically Pleasing. …
• Protects and Decreases Wear & Tear.

How long do epoxy floors last?

10 to 20 years   Long-Lasting, Environmentally-Friendly Floors Epoxy floors typically last 10 to 20 years and can last even longer with the proper maintenance and touch-ups. When it finally comes time to replace your floor, there will be no need for removal, and no need to throw away your old flooring.