Can I "PATINA" an Engelmann Spruce Top?

[BothHands]

Recently I bought two nearly identical used Alvarez Masterworks dreadnaughts:

Both have good-quality Engelmann Spruce tops.
Both were manufactured in 2005 (a few months apart).
Both have the same gloss finish - either a lacquer or some kind of poly/acrylic.

The spruce top on Specimen A has a beautiful "butterscotch tan" color.
The spruce top on Specimen B is more pale - not Stark WHITE like some E.Spruce, but a considerably lighter tan than the Specimen-A top.

Both guitars were purchased USED.
Specimen A (darker) appears to have lived "a more active life" outside it's case and getting played.
Specimen B (lighter) probably slept in it's case most of the time.

Since they were manufactured just a couple of months apart I'm thinking (hoping) exposure to sunlight may be a factor in Specimen A's darker appearance.

Q1. Does SUNLIGHT cause guitar finishes to PATINA (shift from clear to amber). Or is TIME the only real factor? How about HEAT?

Q2. Do ALL finishes patina?

Q3. Can I accelerate the patina on the lighter Specimen B so it "catches up with" Specimen A? If so, HOW?
If SUNLIGHT is the key, can I stand the guitar outdoors facing the sun for short periods of time?
I know excessive heat can destroy an acoustic guitar, so IF sunlight will work, please tell me exactly how to do this without catastrophe.

Q4. If anybody knows what finish Alvarez used on it's Masterworks series in 2005, please weigh in?

Thanks

[John Arnold]

Some finishes yellow, but the catalyzed polyester that dominates Asian guitars is one that does not very much.
What you are seeing on the darker top is probably tanning of the wood itself, which is primarily due to UV exposure.
You can get this with sunlight, but you need to make sure you are not overheating the guitar. A safer way is with a couple of 24" long fluorescent UV tubes.

[BothHands]

John ==
Thanks for the help. Replies to such inquiries seldom turn out to be good news, but in this case all three points you make seem to be exactly what I want to hear. Please allow me to double-check the details before I do anything potentially harmful/stupid:

Originally Posted by John Arnold

[...] the catalyzed polyester that dominates Asian guitars is one that does not [yellow] very much.

These guitars were made at a Chinese factory in 2005, so they certainly are Asian. From a durability standpoint, (I think) I'm delighted to find out they're "catalyzed polyester". I know some insist on lacquer--nitrocellulose or other--but I'm willing to give up the potential benefit for a more robust, less delicate finish.

Originally Posted by John Arnold

What you are seeing on the darker top is probably tanning of the wood itself, which is primarily due to UV exposure.

So you think the gloss finish is not being affected by UV exposure, but THE WOOD ITSELF has become slightly darker and/or richer in color from UV exposure. Is that right?

Originally Posted by John Arnold

You can get this with sunlight, but you need to make sure you are not overheating the guitar. A safer way is with a couple of 24" long fluorescent UV tubes.

Man, if I can do this in a controlled and safe manner by using fluorescent tubes, that will be GREAT(!).

1. I have a pair of Sylvania 20watt 24" GRO-LUX grow lights. Will they do the trick?

2. I also have some 5500K sunlight equivalent CFL bulbs that I use for photography and video lighting. Here's a link. Would two of those in front of the guitar body be the better choice?

3. Or is some other type of 24" tube necessary?

Do you have any idea how many hours of exposure will be needed for a subtle change in color? Are we talking 10s of hours or 100s of hours?

Many thanks.

[John Arnold]

So you think the gloss finish is not being affected by UV exposure, but THE WOOD ITSELF has become slightly darker and/or richer in color from UV exposure. Is that right?

Yes. This will be evident if the guitar has white binding. On guitars that have a yellowed finish (like traditional nitrocellulose lacquer), the bindings will turn yellow. With the polyester finishes, the binding will remain white.

1. I have a pair of Sylvania 20watt 24" GRO-LUX grow lights. Will they do the trick?
2. I also have some 5500K sunlight equivalent CFL bulbs that I use for photography and video lighting. Here's a link. Would two of those in front of the guitar body be the better choice?
3. Or is some other type of 24" tube necessary?

It's all about how much UV the light emits. I have only used regular blue UV lights, so I don't know how these would work. My gut feeling is that they produce less UV, and will require more exposure to get the same result.

Do you have any idea how many hours of exposure will be needed for a subtle change in color? Are we talking 10s of hours or 100s of hours?

My experience with the 20W blue bulbs is that you will notice some change in a few days, and a significant darkening after a couple of weeks of exposure.

[BothHands]

Very good, John.

The binding is a faux tortoise shell (shiny brown plastic, primarily) so that's not an issue.

A quick stop at Google suggests that "blue UV bulbs" are actually black light bulbs.
Is that the type you mean? Here's an EXAMPLE.

Also, do you happen to know whether natural sunlight through window glass will have the desired affect?
The windows here are basic double-pane residential window glass installed some 20 years ago (so no special UV filter or fancy gas between the glass, etc.)

[John Arnold]

A quick stop at Google suggests that "blue UV bulbs" are actually black light bulbs.
Is that the type you mean? Here's an EXAMPLE.

Yes, UV is commonly called black light.

Also, do you happen to know whether natural sunlight through window glass will have the desired affect?

It does seem to work, but somewhat less UV than direct sunlight. So it will take longer.
http://grammar.yourdictionary.com/st...t-grammar.html

[BothHands]

Thanks a lot, John. I've learned a lot in this thread, and try to learn something new every day.

Today I learned about UV and it's effect on spruce tops, AND a little grammar to boot <blush>. Frankly, I'm unsure about those two half the time, so thanks.

[redir]

I think normal glass blocks UVB but not UVA. UVB is the one that burns you but I think the UVA is also harmful and as such will cause the desired e(a)ffect ( I always get those two mixed up too ). So as such it would take longer.

I don't think it's a good idea to leave a guitar in the sun. Maybe if you are real careful and check the surface temperature or just do it in the early evening at least.

Modern glass may be treated to block most UV light so if your house is new with new windows then it may take even a lot longer. I don't know, I'm just sort of thinking out loud here.

[BothHands]

Originally Posted by redir

I think normal glass blocks UVB but not UVA. UVB is the one that burns you but I think the UVA is also harmful and as such will cause the desired effect [...] it would take longer.
I don't think it's a good idea to leave a guitar in the sun.
Modern glass may be treated to block most UV light

Thanks for chiming in. I don't like buying any more "stuff" than necessary, and since I don't expect to "patina" any guitars other than this one, I'd like to find an alternative to buying black light tubes.

I don't like the idea of leaving a guitar unattended outdoors - wind could blow it over, it might overcook, it might rain, birds might nest in it , ANYTHING could happen.

So my first/best choice appears to be sunlight indoors through window glass. As mentioned before, the windows are double-pane and at least 20 years old - so should involve no intra-pane gases or special UV filtering. I'll try it for a while and see how she go...

[redir]

It would very interesting if you took a pic every day over the next how ever many months and composed a time lapse

Even top wood that I have stored away from light gets darker over time. I'm always surprised when I grab a ten year old top out of the pile and plane the surface off and it comes back so much brighter.

Hmmm, pre-patina top wood, I'm sure it's been done before. But I could prep some tops right down to the finish stage and let them sit for years before using them. Marketing genius thanks for the ideas!

[BothHands]

Originally Posted by redir

It would very interesting if you took a pic every day over the next how ever many months and composed a time lapse

That's a very interesting idea and I'll try to do it. It would be instructive for others, but also would provide me a very reliable method of knowing what has (or hasn't) occurred.

Originally Posted by redir

Even top wood that I have stored away from light gets darker over time. I'm always surprised when I grab a ten year old top out of the pile and plane the surface off and it comes back so much brighter.

Hmmm, pre-patina top wood, I'm sure it's been done before. But I could prep some tops right down to the finish stage and let them sit for years before using them. Marketing genius thanks for the ideas!

That's one of the things I like most about online user forums. You just never know how someone else's idea or off-hand comment might spark your own imagination. Rock on!