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Fading of paints


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Early paint formulations tended to fade and/or brown in strong sunlight. The binder in the paint could yellow or brown, just like old varnish can. The surface of the binder could also become chalky, fading down the underlying colour. If a dye or artificial pigment were used to give colour, that might be broken down by the UV, causing it to fade. If the colour was a mixture, different components could fade at different rates, leading to dramatic changes in hue. Flying at modest altitudes in strong sunlight, it could all happen quite quickly.

One example was famous DH.88 Comet racer G-ACSS which, after being wrecked by the RAF (as K5084) was rebuilt by Essex Aero and painted Cellon "Morning Mist" grey. The Burberry clothing company were famous for their beige trench coats. By the time they came to sponsor it, copilot Mrs. Betty Kirby-Green quipped that "when it arrived, it was already Burberry beige."

Some camo paints were brewed up locally, using whatever was available to create a best guess at the official specified hue. Paint batches mixed from different source materials, even if a close match initially, would have faded differently. Even the solvent used to thin the paint would have affected the rate of yellowing/browning (never use cheap solvents on your models, folks!).

But right now, I am interested in what happened to WWII RAF Azure in strong sunlight. It would have been applied at the factory, to the approved formula. Would it have changed in hue as it faded, becoming say greener or duller?

Edited by steelpillow
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2 hours ago, steelpillow said:

I am interested in what happened to WWII RAF Azure in strong sunlight.

Azure probably aware (oh come on, you knew I wouldn't be able to resist) lightfastness tends to depend upon the pigments used.
Blue pigments on the whole tend to be pretty good at holding their colour.
Dyes are notorious for fading

I've done a quick google but have been unable to find which pigments were used in the RAF Azure Blue.

Would have though the undersides wouldn't be affected by the sun anyway.
How much the lower fuselage sides would fade I wouldn't like to say. 

On the other hand there may well have been fading caused by abrasion from dusty North African airfields 

 

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5 hours ago, Walrus said:

Azure probably aware...

Now that my eyes are refocusing after banging my head on the keyboard... Undersides get much affected, especially during the dawn and evening flights, which tended to be the usual. Even on the ground, reflected glare and scatter are strong in sub/tropical countries (actually thinking Northern Territory rather than North Africa, but it's the same difference). I'd hazard that the Azure would fade to a bluer shade, losing its pristine hint of green.

Anyway, I just stumbled on this interesting page: http://www.theworldwars.net/resources/resources.php?r=camo_rafww2

I have a tin of Humbrol 157 from their relatively recent (few years back?) change of heart from the overly dark shade to - and I just ran up a sample - something a bit too pale and so lacking in green it has faintly purple overtones (The lid is in the old shade, the innards in the new - gave me a surprise when I first opened it!). Methinks 'tis a dead ringer for a faded Azure, unless anybody knows better. I might add a touch of light grey to dampen its brightness, um...

Edited by steelpillow
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Posted (edited)

Closely related to the fading of paints is the fading of willpower.

There you are, readying Spitfires for battle all day long. Then some bureaucrat changes the colour of the paint, so machines coming back from the repair depots suddenly start looking all dressed to party. Presently, you are surrounded by a mix of operational machines in one or other scheme. Then you have to order up some more disposable slipper-type drop tanks (winding up your CO something rotten cos he once notoriously dropped one on the houses below). This is where the fading of willpower comes in; assuming the local manufacturer can still find tins of the old paint anyway, do you get them in a mix of colours to match the mix of undersides, or do you utter a naughty word followed by "it" and order the whole lot in the new colour? I mean, if the new camo is so much better, an older machine will just look like it has a big square hole in it, won't it? (bit like that suburban roof back in Sydney, Sir). Or you would not bother at all, on the grounds that it doesn't need a long sell-by date and by the time the enemy look up it will have been dropped off anyway?

'Cos that's where I have got to with my first Aussie Twinfire. Advice welcome. Knowledgeable advice even more welcome. (non-suicidal comebacks to an angry CO most welcome of all).

Edited by steelpillow
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Posted (edited)

Aha! Found some nice photos in the Australian War Memorial collection. The tanks were not disposable as I thought, but got refurbished. I suppose they sent out a launch or ute (utility vehicle, known to us Pommies as a pickup truck) as appropriate under the flightpath to bring 'em back. And a fine mix'n'match range, too. They didn't pretty 'em up again either - the last photo is the CO's machine, and I'll bet nobody dared say it was in that state because it had been pulled out of the master bedroom after dropping in on a Sydney couple without the master of the house's consent.

4107167.JPG

4047942.JPG

4002790.JPG

Killer-Caldwell.JPG

Edited by steelpillow
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Posted (edited)

Now here's another fun game. Humbrol white enamel. The gloss used to be worst at it, while the matt seems to have picked up the habit lately. The stuff browns with age. I have a 30-year-old model I sprayed Humbrol gloss white, and now it is a kind of dirty magnolia. But I also have tinlets of both gloss and matt bought just a couple of years ago. OK they may have been in the shop a while, but that is no excuse for the stuff  turning a rich cream colour while still in the tin!

This is actually quite handy for white recognition strips on my Aussie Twinfires that have been attacked by strong sunlight, but a reet pain in t' proverbial for the spanking new bits fabricated by the ARD. Living here out in the sticks, can I be bothered to drive 20 miles or order online and wait for Godot, for somebody else's matt white?

I'm also mixing up some underside Medium Sea Grey for the Mk eight-eight and I'll swear my collection of light-to-medium grey tinlets are browner than when I bought them, too. So even if I do add some Azure and a dash more of the lighter tones, how is that going to look in another couple of years? Ee, et's enough ter mek yer buy forrin.

Edited by steelpillow
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  • 1 month later...

So, there is a shortage of white paint among local hobby suppliers; note belated datestamp on this post. Eventually I got some matt white PolyVine "acrylic enamel", fresh from the supplier and removed from the packaging in front of my eyes. Next one each of Revell enamel and Tamiya acrylic, and Revell semi-matt for good measure.

Verdict: PolyVine and Revell matt are as magnolia-tinted and useless as the Humbrol. Revell semi-matt and Tamiya matt are better but still distinctly warm whites - at least more single cream than clotted. In some cases the pool of clear binder/solvent on top, that has to be stirred in, was an alarmingly strong brown (like Humbrol "clear" varnish, did I mention that?). Tamiya squeaks the whitest podium, but none is a patch on a proper artist's tube of acrylic or oil paint.

What is wrong with modelling paint manufacturers? Do they hate their customers or all subcontract its manufacture to the same supplier or what?

Still, it is some consolation that in the middle of WWII, RAAF Aircraft Repair Depot 14 would, like all of them, have suffered severe paint shortages and had to settle for less than perfect. Tamiya will probably be an acceptable match.

But, sheesh!!! 🚮 🚮 🚮 😡

Edited by steelpillow
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Pure white paints are something of a grail thing, if you find one, let us know! In enamels it's more in hope than expectation, acrylics are a better bet and generally they will stay whiter, longer, but there's no guarantee. I have a Concorde model that was painted in Tamiya acrylic and it's gradually turned creamy white. Even in the 1/1 world it's a problem.  

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There really is no excuse.

Small drops of "blue whitener" - unless they are fluorescent like washing powders - make the thing a shade of grey (As a kid I used to have a lot of underwear like that, but I don't expect y'all want to go there).

A tube of artist's traditional Titanium White is a pretty good bet, and there are some other similar bright whites around too. If Rowney or Windsor & Newton can cut the mustard, as they say, I really don't see why runnier preparations with a dash extra thinners in can't. If these planes had a new- or show-quality paint scheme, I'd be trying that route.

And ninthly (metaphorically), why don't decal manufacturers match the available paints? It's painful to see them alongside each other; I have had to run a brown wash over all my roundels. Even cheap acrylic emulsion housepaints do a better job. Humbug!

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What I do know is that Alex Henshaw did the drop tests on Spitfire slipper tanks to ensure good separation

over the Cardigan Bay Ranges flying out of Blaenannerch(RAF Aberporth)airfield BITD.

As to what colour they were I haven't got a clue,but I bet they ain't fared well on the seabed of 

Cardigan bay for a good 70-odd years.

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"Killer" Caldwell did similar tests over Sydney for the RAAF. He managed to drop one through the roof of a private house in the suburbs.

A travelling friend once told me that in Japan everyone is so crowded they have to be impeccably polite and never get in each other's way.* But in Australia where there is nobody to see on a vast, empty plain stretching to the horizon, you will suddenly get sent flying by someone barging into your back with a "sorry cobber, didn't see you there!"

* This was before the days of the bullet trains with their automatic doors. There has to be an exception that proves every rule.

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1 hour ago, steelpillow said:

A tube of artist's traditional Titanium White is a pretty good bet, and there are some other similar bright whites around too. If Rowney or Windsor & Newton can cut the mustard, as they say, I really don't see why runnier preparations with a dash extra thinners in can't. If these planes had a new- or show-quality paint scheme, I'd be trying that route.

And ninthly (metaphorically), why don't decal manufacturers match the available paints? It's painful to see them alongside each other; I have had to run a brown wash over all my roundels. Even cheap acrylic emulsion housepaints do a better job. Humbug!

It's that extra dash of thinners that is the problem, that's the bit that goes yellow. If you lightly sand over yellowed white it should come up properly white again.

With regard to colour matching decals, it's a nightmare and in any case no two batches of the same colour are likely to be identical. For graphic artists, they usually had to call for the printer to use the nearest Pantone match, I'm not sure how it works these days, especially as silk screen printing is now old hat. You still have to work with whatever colours you have on the palette of whichever graphics programme you're running.

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1 hour ago, Paul Brown said:

It's that extra dash of thinners that is the problem, that's the bit that goes yellow. If you lightly sand over yellowed white it should come up properly white again.

With regard to colour matching decals, it's a nightmare and in any case no two batches of the same colour are likely to be identical. For graphic artists, they usually had to call for the printer to use the nearest Pantone match, I'm not sure how it works these days, especially as silk screen printing is now old hat. You still have to work with whatever colours you have on the palette of whichever graphics programme you're running.

Not convinced.

Modern turpentine substitutes don't brown with age, never mind the hi-tech thinners supplied for artists' acrylics. Modern paintings keep their pristine finish pretty much indefinitely, there is absolutely no reason why modern models can't either.

Pantone reference is unlikely to be available for an off-white paint that is not the colour claimed. There are lots of Pantone colour pickers out there to specify a suitable off-white. And I never yet met a graphics app that would not let me mix my own colours, and save out a custom palette if I felt the need. The only aspect I don't know about is buying the matched ink, but as the trend these days for short print runs is hi-res CMYK inkjets, that will probably not be an issue.

Edited by steelpillow
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3 hours ago, steelpillow said:

Small drops of "blue whitener" ... make the thing a shade of grey

If that happens it was too much blue. But if getting paint to behave was easy modelling wouldn't be near as much fun.

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11 hours ago, Jessie_C said:

If that happens it was too much blue.

That is quite wrong; achieving a neutral grey defines the exact correct amount of blue. Any less and you get a tinted mushroom colour. But we have grumbled about colour mixing long enough here, it's time we moved on.

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  • 1 month later...

Just found this thread - do you want the full paint chemist and formulator spiel?

On 17/02/2022 at 09:20, steelpillow said:

But we have grumbled about colour mixing long enough here, it's time we moved on.

 

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Posted (edited)
40 minutes ago, Lost Cosmonauts said:

Just found this thread - do you want the full paint chemist and formulator spiel?

 

Have to say, I have now painted my model in a dodgy "faded azure" (see original post above), and moved on. However I have no objection to being informed how bad a choice I made!

And of course, a general spiel will surely be of wider interest to all.

Edited by steelpillow
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On 28/12/2021 at 15:53, steelpillow said:

 I'd hazard that the Azure would fade to a bluer shade, losing its pristine hint of green.

 

I'm very late to this, but last year you said the above.

Azure has no green whatsoever. It leans on the red side of blue giving it a violet quality.

Typical CIELAB values would be somewhere around L64 a-1.76 b-23.65. The negative a-value means it has a red component, not a green component.

ACRN-34_540x.jpg?v=1621431101

I'll try to get the pigmentation of the original. Can I assume the context of interest is metal skinned aircraft using lacquer paints rather than fabric skinned aircraft?

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20 minutes ago, sovereignhobbies said:

'll try to get the pigmentation of the original. Can I assume the context of interest is metal skinned aircraft using lacquer paints rather than fabric skinned aircraft?

I, for one, would be very interested in this. 

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