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WHY RESIN TURNS YELLOW? Is there a solution for it?

WHY RESIN TURNS YELLOW? Is there a solution for it?

Why does resin turn yellow? What can I do about it? What do you do with yellow resin artwork? And - can you still use yellow resin or can it go straight into the trash?

Hello my dear resin friends! Here is your MRS.COLORBERRY again with a new, very interesting blog post about "Yellow Resin!".

For all of you who don't know me yet: my name is Steffi - but better known under the pen name MRS.COLORBERRY and I founded my own company COLORBERRY in 2017 for high-quality resin products. I myself am an entrepreneur, but also a resin artist and have been involved with resin on a daily basis since day 1 of my resin career. So, glad you're with me - let's get started! Here I share my knowledge!

One of the TOP questions I get asked all the time is "Does COLORBERRY resin get yellow?"
Unfortunately, you can't just give a blanket YES or NO answer to this question. Okay, that's a bit of a fib now, because if I'm honest there is a clear answer to this - namely YES! But wait! There is the YES written very small, and there is the YES written very big with an exclamation mark, because, as you can guess now, the classic answer comes to rather extensive answers: It depends!

So let's talk about a bit of basic knowledge first.

Epoxy resin can yellow over time, which is mainly due to 4 reasons: UV radiation, aging, heat and wrong pigments.

Prerequisite when buying good epoxy resin

For epoxy resin, two main ingredients are usually responsible for yellowing:

1. resin component: The resin component of epoxy resin usually consists of epoxy resin monomers such as bisphenol A (BPA) or epichlorohydrin bisphenol-A (EPCB). These resin monomers may oxidize and turn yellowish over time due to UV exposure or chemical reactions.

2. hardener component: The hardener component of epoxy resin usually contains amines or amine compounds. These amine compounds can also contribute to yellowing, especially if they react with UV radiation or chemical compounds in the environment.

It is important to note that the exact composition of epoxy can vary from manufacturer to manufacturer, and various additives and modifications can be used to minimize yellowing. For example, some manufacturers use UV stabilizers or antioxidants to minimize yellowing effects.
So what do you need to look for when buying epoxy to somewhat prevent or minimize the yellowing effect:

Ingredients such as.
1) UV absorbers
2) HALS additives

HALS stands for Hindered Amine Light Stabilizers. It is a class of additives used in various plastics, including epoxy resins, to protect them from the harmful effects of UV radiation.
HALS additives act as free radical scavengers and absorb high-energy UV radiation. They prevent or slow down chemical reactions that can be triggered by UV radiation. The use of HALS additives can reduce the yellowing of epoxy resins and maintain their physical and optical properties for longer.
These additives offer high efficiency in stabilizing plastics against UV radiation and have a long service life. They are able to regenerate through redox reactions and therefore can continue to be effective after repeated exposure to UV radiation.
It is important to note, however, that not all epoxy resins contain HALS additives out of the box. However, some manufacturers offer special UV-stabilized epoxy products that already contain HALS additives to provide improved UV resistance and color stability.
If you are using epoxy and want increased UV resistance, it is advisable to look for products specifically formulated with HALS additives and advertised with UV-absorbers.

All of our COLORBERRY resins have both of these additives and are therefore of high quality. So if you already have COLORBERRY Resin: You did everything right!

So much now for the chemical compositions and basic properties of high quality epoxy resin.

The only question is: Why does the epoxy resin sometimes turn yellow?

As already briefly mentioned above, there are basically 4 things.
So let's talk briefly about point #1: Aging of the resin (in the canister).

Generally, epoxy resins have a shelf life of between 12-24 months and should not yellow during storage - but if they do, it should be minimal.

Even if the epoxy resin is not exposed to direct UV radiation during storage, it may yellow over time. This can be caused by oxidation and chemical reactions that cause the resin to lose its clarity and color stability.

  • Use high quality epoxy: Choose a high quality epoxy from a trusted manufacturer. High quality resin often contains stabilizers and additives that minimize aging and yellowing (we already talked about this in the first point above).
  • Store epoxy properly: Epoxy should be stored in a cool, dry place, preferably at room temperature. Avoid extreme heat or cold, as these can accelerate the aging of the resin. Especially often, long transport distances are also very bad for epoxy resins, because, for example, resin is stored in summer at manufacturer, then shipped over Wohen on the high seas at sub-zero temperatures, only to come back to a warm storage hall.
  • Avoid chemical exposure: Certain chemicals such as cleaners, solvents or acids can attack the epoxy and cause yellowing. Avoid contact with such substances to prevent yellowing.

So make sure you store your resin well and maybe it makes more sense to go to the nearest retail store to get your resin right there.
You can buy COLORBERRY resins in USA (Blick Art Materials), Canada (DeSerres), Kuwait (Al Sanafer), etc... Just send us an email if you want to know if COLORBERRY products are sold near you.

But now to the next influencing factor, which can be responsible for the yellowing of resin: The dear sun - UV radiation

UV Radiation: Epoxy resin is susceptible to UV radiation, especially the resin it contains. UV light can alter the molecular structure of the resin and cause it to turn yellow. Resins without UV stabilizers (UV absorbers + HALS additives) are particularly susceptible to yellowing.

  • Use UV stabilized epoxy: Choose an epoxy specifically designed for outdoor use or for applications exposed to UV radiation. These resins contain additives that can minimize the effects of UV radiation and prevent yellowing. But beware: there is no such thing as a non-yellowing resin - these additives only minimize yellowing!
  • Protect the epoxy resin from UV radiation: please never lay, hang, place your resin artwork in direct sunlight. Not only can it cause the epoxy resin to soften (etagere cast from resin can bend), but it will also accelerate the yellowing process. If you are selling resin artwork, it is advisable to tell the customer this as well. Better yet, write it into your terms and conditions and ask the customer to read it. Or it is directly in the purchase contract.

A very personal tip for all who sell their resin art professionally. If the resin is already cured (so we are talking specifically about finished, cured resin art), you can protect it with a protective coating. Paint or coat the resin with a UV-resistant clear coat (e.g. from the car industry). This layer blocks UV radiation and prevents the epoxy resin from yellowing. Just ask around for paint shops in your area. However, I can tell you right away that this additional layer on your artwork is not cheap and has many advantages and disadvantages. One disadvantage is that all matte areas on your artwork, such as sand or polymer plaster rocks, automatically become high-gloss - so the look of your resin artwork could be lost.

So let's go directly to the 3rd reason that leads to yellowing of the resin: Heat!

Heat during application can also be a contributing factor to yellowing epoxy. High temperatures can accelerate the chemical reactions that lead to yellowing.
When mixing and curing epoxy, it is important to follow the manufacturer's instructions for recommended temperature. If the resin is overheated, it can lead to accelerated aging, which manifests itself as yellowing.

Here are some tips to control heat while applying epoxy:

  • Did you know that we actually make one of the biggest mistakes as resin artists? But it's actually rarely talked about because there are very rarely any good alternatives. Removing air bubbles with heat. Please be insanely careful when dealing with added heat with a heat gun or a Bunsen burner. It can happen so quickly and easily here that you literally burn resin. With this artificial added heat, we can intentionally destroy some chemical compounds that lead to faster yellowing. So please don't overdo it here and alternatively try using COLORBERRY's BUBBLEBYE.
  • Observe room temperature: Make sure that the ambient temperature in the room where you use the epoxy resin is not too high. Keep to the temperatures recommended by the manufacturer for mixing and curing the resin.
  • Use appropriate tools: When mixing and applying the epoxy, use tools that are not prone to heat transfer. Metal tools can heat up considerably and increase the reaction rate of the resin. Plastic tools or tools with low heat conductivity are preferable. So if you don't have our plastic mixing sticks ( 4EVERSTICKS) yet, now would be an optimal reason to do so.
  • Limited working time: epoxy resin often has a limited working time before it hardens. If you are using the resin in a hot room, this time may be shortened. Therefore, work in sections and mix only the amount of resin you can use within the specified working time.
  • Use cooling options: If you are working in a hot environment, you can use cooling options such as fans or air conditioners to lower the room temperature and reduce the heat stress on the epoxy.

However, I would like to revisit a very important issue here, which is the deliberate letting of fully blended epoxy resin stand until it reaches the desired viscosity. It is unfortunately common in the resin world to simply let thin-bodied resin sit until it begins to cure and become thicker! This is truly bullshit when you consider that in the mixing cup during this exact time, the exothermic reaction is already destroying the chemical compositions and then your artwork will turn yellow even faster in the aftermath. So it does not always have to turn yellow immediately, but can also lead to a faster yellowing process afterwards. Please use a resin that already has the desired viscosity.

By controlling the heat during the application of epoxy resin and keeping to the recommended temperatures and processing times, you can reduce the risk of yellowing due to heat exposure.

And what about color pigments? Do they affect the yellowing of resin?

Yes, the wrong color pigments can also cause yellowing of epoxy. If inferior color pigments or those not suitable for epoxy are used, they can cause discoloration or yellowing.
To avoid yellowing caused by color pigments, you should observe the following points:

  • Use high quality color pigments: Select color pigments that are specifically designed for use in epoxy. High quality pigments are usually more stable and less prone to discoloration or yellowing, such as our dry powders (CARAT COLLECTION) or RESIN PIGMENT PASTES.
  • Pay attention to pigment compatibility: not all color pigments are compatible with epoxy. Certain pigments, especially oil-based or water-soluble pigments, may undergo undesirable chemical reactions with the resin and cause yellowing. Use only pigments that are labeled as epoxy compatible. 
  • Follow dosage recommendations: Excess or insufficient addition of color pigments may cause undesirable reactions. Follow the pigment manufacturer's dosage recommendations and add the pigments to the epoxy resin in the recommended amount.
  • Test pigments beforehand: Before you start the epoxy resin project, you should carry out a test run with the desired color pigments. Prepare a small amount of resin with the pigment and let it cure to make sure there is no yellowing or discoloration.

By using high quality color pigments suitable for epoxy and following the dosage and compatibility recommendations, you can reduce the risk of yellowing from color pigments.

So what do you do if you have yellow resin in the canisters or if a resin artwork is complained to you because of yellowing?

First, about yellowed resin in the bottles or canisters themselves. Yes, you can use yellow epoxy resin in principle, even if it is yellowed. However, it's important to note that yellow resin loses its original clarity and transparency and has a yellowish tint. This can affect the aesthetic appearance and visual properties of your projects. However, the basic properties such as strength and durability, are intact.
So if you have yellow resin on you - please don't throw it away or discard it. Just use it with darker colors like black, gray, purple, red or dark blue. So basically for any rich colors you want to cast with. However, white, high or clear pours should be avoided with the resin.

But what about yellowed resin art?

Please stop the mytos of thinking you can stop yellowing with another layer of resin - even if this is a resin layer of resin with UV absorbers and HALS additives. Resin is like glass and the UV goes through - so it also goes through to the layer you are trying to save here. You won't like this answer, but unfortunately there is nothing more you can do here. Sanding and recasting with darker colors maybe - yes ...
But there is still a small glimmer of hope:
The only possibility here is to have a painter apply a coat of varnish with UV protection. But this should be done beforehand, especially for very high-priced resin artwork.

As you have now read, there are so many different possibilities why the resin forgives and unfortunately this question, which you ask me so often, can not be answered in one sentence. Just make sure you buy high quality resins, pay attention to the storage conditions, your handling of the resin and the colors used and also the instruction to the customer regarding avoiding UV light.

Thank you for reading and we will hear from you next time. If you have any questions or suggestions about topics that are burning under your nails, just write me an email to help@colorberry.de!
I am looking forward to the next time!