"Yellowed" varnish - any cure?.

[JonKing]

Evening all, hopefully someone can offer me some advice.

 

 

I resprayed these two Heljan 47s into Freightliner Grey around 18 months ago, painting process was fairly standard - halfords primer, phoenix precision top coat, Humbrol gloss varnish (from a rattle can), transfers, weathering and then all sealed with a coat of Humbrol matt varnish (again from a rattle can). Shortly after completion my second son was born and the locos were stored in a display cabinet in my office. Now that the chaos of having a new born has subsided I am "playing trains" again and decided to retrieve these two from the cabinet for a running session. 

 

As you can see from the photos the varnish appears to have yellowed, this isn't noticeable on the dark grey areas but the rail grey is now more like rail beige!. I have decided I cant tolerate this as it just looks plain wrong so the locos have been stripped of glazing etc ready for an appointment with some superstrip and a respray to put them out of their misery.

 

Has anyone had this problem before and can it be rectified without needing a fully respray?.

 

I am blaming the Humbrol varnish however any thoughts on possible alternative causes would be appreciated. (Please bear in mind however, they were definitely rail grey when first painted!).

 

Thanks,

 

Jon

Edited January 18, 2019 by JonKing

[Guy Rixon]

I also find that Humbrol varnish yellows, plus it eats transfers. It's on my list of never-use products. I don't know if it's reacting to something in the atmosphere or whether it degrades in UV light.

[Anglian]

Unfortunately there is nothing you can do other than strip the varnish and paint and start again. I did a bit of research into paints and varnishes having suffered a similar problem. In the course of my investigation I was able to speak with a number of people who worked in the R&D labs of various paint manufacturers, some who produced DIY paints and other model making paints.

They all told me exactly the same thing. Any paint or varnish with an oil or lacquer base has the ability to yellow. That is not to say it will yellow but that it can. To avoid this you need to use acrylic based paints that are based on different types of resins that will not yellow.

Lots of folks will tell you they have used X,Y or Z brand of oil based paints that have never yellowed – they have been lucky but I trust the scientists in the paint labs that I spoke with and now only use acrylic paints and varnishes. If in doubt about a particular paint, get in contact with the maker and ask them.

[JonKing]

I also find that Humbrol varnish yellows, plus it eats transfers. It's on my list of never-use products. I don't know if it's reacting to something in the atmosphere or whether it degrades in UV light.

 

It should be on my "never-use" list due to past experiences of Humbrol Matt varnish drying white, satin drying gloss etc however due to laziness I have continued using it!. This will be the last time.

 

Unfortunately there is nothing you can do other than strip the varnish and paint and start again. I did a bit of research into paints and varnishes having suffered a similar problem. In the course of my investigation I was able to speak with a number of people who worked in the R&D labs of various paint manufacturers, some who produced DIY paints and other model making paints.

 

They all told me exactly the same thing. Any paint or varnish with an oil or lacquer base has the ability to yellow. That is not to say it will yellow but that it can. To avoid this you need to use acrylic based paints that are based on different types of resins that will not yellow.

 

Lots of folks will tell you they have used X,Y or Z brand of oil based paints that have never yellowed – they have been lucky but I trust the scientists in the paint labs that I spoke with and now only use acrylic paints and varnishes. If in doubt about a particular paint, get in contact with the maker and ask them.

 

Thanks for this, very interesting. I have never really got on with acrylic paints finding them difficult to spray and achieve a good coverage, based on the above it seems I should practice a bit more and start moving towards acrylics.

[Steven B]

I've had problems with Humbrol varnish going yellow with the same combination of paint - Halfords primer, Phoenix top coat etc. Switching to the Matt Cote/Satin Cote/Gloss Cote range gave better results.

 

Rather than dunk the model in Superstrip now, I'd be tempted to see if it can be rescued with some weathering;

[davefrk]

In the museum world wooden cabinets are known for discolouring items stored within so it could be where the newly painted loco was confined. Ever wondered why newly cleaned silver bowls get a brown swirly paternation when in a wooden display unit, I know ours do. Some woods are bad for 'off gassing' where the acids in the wood are fumed off over time plus too the fumes from the paint which can still be smelt months after painting.

 

Dave Franks