Fading guitar's....

Discussion in 'Historics & Reissues' started by geochem1st, Apr 1, 2010.

  1. geochem1st

    geochem1st V.I.P. Member

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    How does nitrocellulose lacquer and common dyes used in guitars fade?

    This question has recently been asked of me by a member here and there seems to be interest on how and why this happens, so I put together a basic write up to help explain what goes on. :)

    Almost everyone here knows that 'light' does the fading. But how and why does that happen? Maybe I can shed some 'light' on the issue.

    First we have to understand some things about light and the electromagnetic spectrum, and polymers.

    Light:

    The electromagnetic spectrum is a continuous range of frequencies and energies, with visible light occupying a small portion of the whole.

    [​IMG]

    The sun puts out electromagnetic energy throughout the whole spectrum. What interests us is the visible spectrum and the ultraviolet range.

    In 1887, the photoelectric effect was discovered by Heinrich Hertz, as he was experimenting with radio waves. He was not particularly interested in the phenomenon, but he did notice that the effect was produced strongly by ultraviolet light and more weakly by lower frequencies. Light whose frequency was lower than a certain critical value did not eject any electrons at all. Why is this important?

    A light wave consists of electric and magnetic fields. The stronger the fields, i.e., the greater the wave's amplitude, the greater the forces that would be exerted on electrons that found themselves bathed in the light. Light excites electrons with enough energy to break atomic bonds, but light also enables us to see colors.

    We see those colors because they reflect light back to our eye from very specific parts of the visible-light portion of the electromagnetic spectrum. Unfortunately, what's not reflected is absorbed, and that's where the trouble starts.

    Light is energy, and when that absorbed energy equals or exceeds the so-called 'activation energy' of a molecule in a dye or pigment, the molecule becomes "excited," meaning, rendered available for chemical reactions. If your dye is chemically active, it means it's interacting with the environment and becoming chemically altered. A number of things, many of them destructive, can happen once a molecule gets excited. The extra energy may be converted to heat (infrared energy) or emitted as light (phosphorescence or fluorescence). It can break chemical bonds within the molecule, breaking the dye down.

    Generally speaking, organic materials—those derived from plants or animals—are more susceptible than inorganic materials. For instance, natural dyes, which are organic, generally fade faster than pigments, which are usually comprised of inorganic minerals.

    The older red organic dyes are more susceptible to fading because of the organic chemical makeup and becuase they look red and thus absorb blue, which is the higher-energy light.

    The energy from light can also jump to another molecule. In one of the most damaging of such leaps, the energy transfers to an oxygen molecule, which can then react with other molecules to jumpstart chemical reactions. Oxidation takes place, bleaching out the color.

    But that's not all. There can be synergistic effects: with higher temperature and humidity, for example, reactions catalyzed by electromagnetic radiation can occur more rapidly. And there can be chain reactions: new substances formed as a result of photochemical reactions will have enough energy to also react with the original substance, launching a chain reaction of degradation. Something to keep in mind is chemical reactions initiated by light can continue even after the object is placed in the dark.

    The ultraviolet wavelengths of interest are:

    UVA: 320 - 400nm SKIN TANNING
    UVB: 280 - 320nm SKIN BURNING
    UVC: 100 - 280nm INDUSTRIAL GERMICIDAL USE.

    All types of UV can cause a photochemical effect within the polymer structure. It is the high energy UVC wavelengths that are produced by the Sun, and not by artificial lights except in industrial use that cause the most degradation to polymers.

    Polymers:

    Lacquer refers to polymers dissolved in volatile organic compounds (VOCs), such as nitrocellulose, and later acrylic compounds dissolved in lacquer thinner, a mixture of several solvents typically containing butyl acetate and xylene or toluene. A polymer is a long chain of molecules that repeats a pattern of atoms. These molecular groups are tied together through bonding of electrons.

    Like with dyes, one of the main problems of considering the effect of UV rays on polymers is the intensity related to: stratospheric ozone, clouds, altitude, the position of the sun height (time of day and time of year), and reflection.

    The main visible effects in polymer degradation are a chalky appearance and a color shift on the surface of the material, and the component surface becomes brittle. Often a fluorescent whitening agent (FWA) is added to the polymer. In natural light many polymer products can appear to have a yellow appearance. But by adding a FWA the UV light absorbed is then emitted in the blue region of visible light (400-500nm wavelength), instead of the yellow region. When we shine an UV flourescent light on a finish to check its consistancy, this is the blue light that we see from this additive.

    As the polymer breaksdown over time and exposure, the color returns to the yellow that we associate with 'old' nitro finishes.

    UV energy absorbed by polymers can excite photons, which then create free radicals. While many pure polymers cannot absorb UV radiation, the presence of catalyst residues and other impurities will often act as receptors, causing degradation.

    Only a very small amount of impurity may be needed for the degradation to occur, e.g. trace parts per billion values of sodium in polycarbonate will initiate color instability. In the presence of oxygen the free radicals form oxygen hydroperoxides that can break the double bonds of the backbone chain leading to a brittle structure. This process is often called photo-oxidation. However, in the absence of oxygen there will still be degradation due to the cross-linking process.

    As there is an interest in artificially aging guitars, a few things have to be considered. Many of the lacquers used in the 1950's are not of the same formulae as todays. Many new UV blockers, plasticizers, and stabilizers have been added. UV bulbs do not produce the same spectrum as the Sun, so the results will not be the same. As with the lacquers, todays dyes have more inorganic components to stabilize them than in the past.

    I hope that this has been helpful.
     
    tspoon5150, jcsk8, IGRocker and 35 others like this.
  2. Penny Dreadful

    Penny Dreadful Banned

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    Great post!...I have a heritage cherry that id like to fade a bit.
    Perhaps play outside in the sun for about 15 mins a day. lol

    I know it wont fade as the old ones did, but time will tell.
     
  3. mudfinger

    mudfinger Thanks for the memories! V.I.P. Member

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    Gonna take a while to wrap my head around this, but thanks very much for the post, Geo! :thumb:

    I've had my guitar in the sun almost daily for a couple weeks now, and the only change I've been able to discern is with the clear/amber area on the belly of the guitar top. I didn't notice that change until I pulled the pickup rings off, might not be from the past couple weeks even. It's getting lighter.

    From what I've read in your post, I'm thinking that the amber dye is fading faster than the nitrocellulose lacquer is yellowing, and the red dye is so well protected by additives that it's not fading at all, or so slightly that I can't tell. But it also seems like at some point, the UV blockers and plasticizers themselves will start to break down, and eventually, the nitro will yellow, and the red will break down to something else, whatever that something else may be.

    I'll keep thinking. :laugh2: When it comes to whitening agents, you did mention that they eventually break down, so it sounds to me as if the real challenge to aging newer guitars is getting the red dye to break down.

    Wow, Geo, thanks again. :applause::applause::applause:
     
  4. lp_junkie

    lp_junkie Senior Member

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    Awesome post, but too much science and facts not enough magic pixie dust.
     
  5. Mike60

    Mike60 V.I.P. Member

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    here we go again....
     
  6. GuitarGuy503

    GuitarGuy503 Senior Member

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    Not this again..... :io:
     
  7. GuitarGuy503

    GuitarGuy503 Senior Member

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  8. R8R6Ben

    R8R6Ben Senior Member

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    Thanks:) very informative.... i wish we could gather info on the various types of formulas used to finish the guitars then we could simply spray a few test strips and expose them to different types of light to determine which would be the best frequency to fade specific types of finishes
     
  9. tunanut13

    tunanut13 Senior Member

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    This has the making of great PhD research ! :)
     
  10. mudfinger

    mudfinger Thanks for the memories! V.I.P. Member

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    I guess some people are content with reading the various extant threads, which is cool, but I'm very interested in the science behind fading, which hasn't been explained until this thread...

    I know Mike has faded some guitars using natural sunlight, and the results look fantastic. These are newer guitars, presumably with at least some UV blockers in the lacquer. I've read a couple of threads recently in which people were considering using artifical UV light, which seemed a bit dodgy to me at first glance, and which actually does produce a different result than fading by sunlight, because all the artificial UV sources create UV at very specific frequencies, wheras sunlight is broadband, so to speak.

    Not sure if it was on MLP or not, but one guy somewhere said he "blasted" his LP with so much UV that the plastic partially disintegrated. True? I dunno, but I'd like to know what he used to "blast" UV, mebbe a tanning bed?

    Right now I'm wondering about how UV blockers work, if they somehow absorb UV for a time and then break down, or perhaps raise the activity threshold of the polymers around them, but remain effective permanently.

    I think it's damned interesting, myself. :dude:
     
  11. geochem1st

    geochem1st V.I.P. Member

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    The best place to gather that sort of info would be in the Luthier's sub forum. My guess is that you probably won't get too far in determining what is actually in the formula. The Luthier's buy a stock polymer base, which would be designated by a manufacturers number, and then thin it down with the proper solvent for spraying.

    Finding out the formula of the stock polymer base in detail would be near impossible as that is proprietary info. The stabilizers and additives that are added to make one finish better than another is valuable info, and separates you from the competition.

    UV blockers work in various ways, the most common being as UV absorbers. What happens with most UV absorbers is that the absorbed energy has to go somewhere. Most of them emit the absorbed energy as infrared, which means the get hot. As shown in my post, heat plays a part in degrading dyes and polymers. The blockers do not prevent degradation, they just slow it down, and they eventually breakdown themselves.

    The red colors, that were mostly organic in makeup, as shown by the 50's bursts (and other models) degraded rapidly, creating 'lemonbursts'. The inorganic pigments that were used on bursts starting in 1960 were made up using a higher percentage of inorganic iron oxides. Depending on the oxidative state of the iron (+2 or +3), the color can vary from a dark red to orange. This change in formula produced a color that lasted much longer, but photo-oxidation processes (as described in the post) would change the +2 (deeper red) pigment to the +3 orange pigment and result in the 'tomato soup' color of the 60 burst that collectors don't like.

    I would guess that todays formulations of the red color would produce the same effect.
     
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  12. joos

    joos Senior Member

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    this might sound really really stupid...if you put your guitar in a tanning bed would it fade it. i like mine the way it is, just throwing ideas out there
     
  13. River

    River Senior Member

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    Great write-up for us laymen. Thanks, Geo.
     
  14. geochem1st

    geochem1st V.I.P. Member

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    Yes it would fade, but not the same way as out in Sunlight.
     
  15. weirdotis

    weirdotis Senior Member

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    What about putting it under a blacklight? Will the fading be more or less extreme for the same amount of time?

    Thanks for taking the time to write this up, really appreciate it!
     
  16. geochem1st

    geochem1st V.I.P. Member

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    'Black Lights' of the flourescent variety, typically peak at around 370 nm, which puts them in the UVA range, the weakest of the UV's energy wise.

    The fading depends on various conditions, including heat, humidity, light intensity, etc, but its fairly safe to say that the fading will less intense and different compared to Sunlight given the same exposure times... but that will also depend on where you live and the angle of Sunlight, which affects light intensity.
     
  17. Penny Dreadful

    Penny Dreadful Banned

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    I was thinking about leaving it out in direct sunlight for about 20 mins a day for
    a week. Ill leave the pickguard on, so if there is any fading youll be able to see
    it if its removed.....I will however cover the neck and headstock and also cut out
    cardstock in the same shape as the pups and lay them on top. I dont want the pups
    to heat up too much.......who know what will happen. lol
     
  18. geochem1st

    geochem1st V.I.P. Member

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    It's going to take a lot longer than that to see results. You are up in Ontario, not exactly known for intense sunlight. The 20 min exposure is good, I think one week is way too short.
     
  19. Penny Dreadful

    Penny Dreadful Banned

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    No offence intended, but it gets very hot up here. Especially from late June untill
    early September. Im near Niagara Falls, so any western New Yorkers here will vouch
    for me...there are times it gets brutal!
     
  20. River

    River Senior Member

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    Yes, but the angles are low up there, and the air thick. Down here in southern Colorado, up at 8,000 feet, I'd bet the sun would do at least four times the job. I would fear for a guitar left out in direct June/July sun for any real period time. I wouldn't be surprised if the plastic parts started to disintegrate.
     

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