Hello all.

I'm reasonably sure that most have had issues with their epoxy hardener yellowing in storage.
Is anyone aware of the manufacturers using an inert gas purge on their filling lines ?
The yellowing seems to start after first opening the container and exposing the product to air.
Prior to opening the product looks clear and the time on shelf may have been days, weeks, months or years.
If the product is affected by exposure to air, then a flush with gas prior to re-capping would address the issue.
Are epoxy hardeners brand specific to brand resins ?
Can any brand hardener be used with any brand resin ?
Perhaps the hardener should be sold separate from the resin in smaller container sizes ?
I realize this would curb sales of kits or possibly the kits should be available with 1 container of resin and 2 smaller containers of hardener ?
It's still only 10 cents of product in a 25 cent bottle selling for 10 dollars.
Maybe a little less profit or you can pass the extra cost along as a convenience feature.

Replies are appreciated as this is not my field of expertise.

Eugene Moore

Eugene

Don't know about inert gas but I doubt it. Hardener will yellow in unopened bottle.

Mixing brand A resin with brand B hardener is a bad idea. Unless you are a chemist with detail knowledge of each brand's chemistry you are the odds on favorite to make a mess.

Yes, purchasing smaller quantities does help, but good luck buying resin and hardener separately.

All spar varnish (long oil) and epoxy will eventually yellow on the rod - it's a rule in our UV world. Your yellowed hardener might not be so bad. Mix up a batch and try it. You just might find the mix is clear and cures clear.

All hardeners will yellow or amber over time. And... UV inhibitors, which many hardeners contain, are themselves a bit yellow or amber.

Even new, mostly clear epoxy hardener will yellow or amber AFTER it has been mixed, applied and cured on the wraps. So starting with new, mostly clear hardener does not solve the yellow/amber problem. It's still going to happen, either in the bottle, or on the rod.

.............

The yellowing is caused by UV light, not exposure to air.

So the answer is It's going to happen over time anyway. Therefore it's not important and "good enough" for the build of a custom rod.
I can't be responsible for the effects of time and use. I can be responsible for the quality of the finished rod I've built.
I'd prefer not to supply a built to order, brand new rod with already yellowed finish.
I'll just throw the finish away and buy "fresh" and pass the costs along. Will need to buy the smallest size available and wait for shipping.

Gene

Unless the hardener is extremely dark, when mixed with the resin and applied thinly on wraps, it is not noticeable. The exception would be on a white surface. If you examine older builds that have been exposed to sunlight, you will find it difficult to observe the yellowing.

To slow down the yellowing process, keep your supply in dark storage, mine is a drawer.

In my opinion Thread Master yellows much less than any other epoxy finish I have used. If you want something that never yellows use Permagloss. Requires several coats to get a smooth finish, and it is very hard, but will never yellow.
Norm