Active corrosion affecting Les Paul

[Leo_Gnardo]

It wouldn't be the first fungus to eat a stringed instrument. I think you and I covered that on another thread though

You remember the story of the Taylor K55C that got left in the tour bus bay, with the air conditioner dripping on it for 5 weeks one mid summer. What a pity. I thought that was a fine instrument. When done, it was fit for growing oyster mushies all right.

Mick, maybe this spring & onwards, after all this damp winter, you'll get a bumper crop.

By not knowing until too late I've missed out on some choice morels, oyster, hen-of-the-woods, & who knows what else. OTOH my lawn sprouts some fine amanita muscaria that the squirrels & deer seem to like, sulfur shelf, and some other mystery types that look and/or smell forbidding. I'll stick with the grocery store white buttons for now. Until I find morels again. (Yes I know about the false morel aka vrpa. Hollow stem = real, solid stem = false.) Got some photos though.

[Chuck H]

Morel season is upon us!!! Another couple of weeks and I'll be picking. Part of the game is knowing when, not just where to look. So if you're anywhere near where morels are known to grow a quick internet search for any seasonal/regional info may help keen you into when and where. Maybe it's just your luck that this topic came up right at the start of the season! Free morels are a good thing indeed. And it makes for a good excuse to walk in the woods.

[Enzo]

May is Morel Month in Michigan.

[cbarrow7625]

FWIW, in a previous life I spent 10 years designing and building temperature and humidity controlled chambers for the scientific community. The most important thing that I came to learn about, and manipulate, for maximum benefit to my designs was not Relative Humidity (RH%) but Dewpoint (DP) (Basic Definition: For a given temp, what is the RH that would completely saturate the air; i.e. produce 100% humidity). While RH is a RELATIVE measurement of the ability of air to contain water, DP is an ABSOLUTE measurement of the QUANTITY of water vapor in the air. Here is a great chart that shows the relationship:

http://upload.wikimedia.org/wikipedi...int-RH.svg.png

Translated into non-tech: It shows that a guitar stored at 50% RH @ 35C will encounter the same amount of moisture in the air as one stored at 100%RH @ 22.5C! Stored at 50% RH @ 30C, there will be the same amount of moisture present in the air as a guitar stored at 20C @ 90% RH! If the wood is dry and encountering moisture, it doesn't really care about RH alone; the dry wood is going to soak up the moisture in the air if it is present. That is why you always hear "Store in a COOL and dry place", not just a "dry" place. Using RH, as most of us do, "Dry" is actually relative and often misunderstood.

As for drying it out, using desiccant is a great idea. However, I would not just buy the disposable silica packs; there are much better (higher capacity) desiccants out there that are also renewable (they can be heated to dry them out & used again). Here is a really interesting device I found on my first search on Amazon:

http://www.amazon.com/Eva-dry-Renewa...ords=dessicant

It lets you know when it is full of water and needs renewing. The color change is typical of this type of desiccant. This one is cool because it has its own built in heating element to renew it but you can also find renewable desiccant in bulk for cheap from scientific catalogs (probably also somewhere on Amazon too) that can just be placed on a tray in the oven that gets renewed in as little as 30 minutes.

I hope this info helps somebody here. Cheers!

[Mick Bailey]

If the wood is dry and encountering moisture, it doesn't really care about RH alone; the dry wood is going to soak up the moisture in the air if it is present.

Doesn't this assume the wood is hygroscopic? I can understand (say) an anyhdrous compound sucking all the moisture out of the air regardless of temperature or RH. My understanding is that there's an equilibrium point - EMC Equilibrium Moisture Content - at which the water in the wood evaporates at the same rate at which it's absorbed and therefore maintains the 6% to 7% 'built' moisture content.

You illustrate that a guitar stored at 50% RH @ 35C will encounter the same amount of moisture in the air as one stored at 100%RH @ 22.5C. This is where I'm missing something; in the first example the air has the capacity to absorb more moisture and 50%RH@35C could well be the equilibrium conditions for the species of timber and construction of the guitar. Does this not render the DP as a predictive, theoretical measurement?

Lets say I have a Taylor guitar. Now I know it's built at the factory at 75F@47% RH. If I maintain those figures, will the guitar not be in equilibrium? I can't see how the actual volume of moisture becomes relevant. If I have a DP meter how would I maintain Taylor's environment? That is, what DP value would I need to maintain?

[cbarrow7625]

Mick, when specifying 75F@47% RH you are specifying a dewpoint (of about 56F). That is the point; looking at the RH alone is not enough if you want to be in the best position to prevent damage and corrosion. You clearly know more about wood behavior than I do and it sounds like my assertions about the wood may not have been correct, my bad. I was actually thinking more about the overall damage to the guitar and thought the wood example was the easiest way to get the point across; clearly I misspoke. So lets think about the corrosion on the metal and pickups; temperature matters to corrosion and metals. Going from lower to higher temperatures with constant, fairly high RH (50-60% and above) metals corrode more quickly. If the dewpoint is maintained as the temperature increases, there is little increase in corrosion as temperature goes up. Why? Smaller amounts moisture particles in the air to interact with the surface. If the temperature is maintained and the RH is increased, corrosion will happen at an even faster rate than when the temp & dewpoint were raised simultaneously to maintain a constant RH reading. Why? The amount of moisture particles in the air and their density of them increased. Density (RH) is more important than number moisture particles, but the number (DP) matters as well.

More importantly, and I didn't bring this up in my first post, if there is temperature variation in the storage space (many of our homes have this to varying degrees) the RH inside the case will increase as the temperature drops. A sealed case can still exchange heat with the outside world but, depending on construction, not all cases will also exchange moisture. If you measure the RH as 50% when it is 35C, what happens if the temperature drops to 25C? The RH inside the case will rise to about 85%, drastically increasing the likelihood of corrosion damage. Think about what happens the other way around; you check the RH to be 50% when it is 25C, what happens when the temperature raises to 35C? The RH drops to 30% and reduces the chances of damage. At the worst extreme, dropping temperatures can cause the ultimate bad thing to happen: condensation. Water droplets directly on the surface of the instrument. Usually this will happen once the temperature starts to go back up and the temperature rise lag caused by the mass of the instrument will remain cooler than the surrounding air, leading to water vapor condensing on the parts (and possibly the wood). I mention it only as an illustrative extreme; I doubt many of us experience this.

Thanks for pointing out where I was wrong and challenging me to provide better examples (and I got to learn something about wood I didn't know!).

[Mick Bailey]

I get quite a few examples of guitars and amps, particularly flight cased, where condensation has occurred - sometimes pretty severe. This mainly happens in the winter where the equipment is put away after a show and left in a van in sub-zero temperatures and delivered to me the next morning dripping wet. I had a cased AC30 a couple of months ago that was so bad it needed dismantling and drying out all day before I could work on it. I was worried about the Celestion Blues that looked like they'd been under the shower. I'm talking really bad here and the owner tells me it was put away dry after a rehearsal.

You make an interesting point about sealed cases (and I'm thinking guitar cases in particular) not exchanging moisture. My original thoughts some time back was that a sealed case would be better in stabilizing the environment. After seeing this particular guitar and my own experience with the Telestar I mentioned, as well as your own observations, this is probably incorrect for the reasons you state. A guitar packed away under seemingly 'warm & dry' conditions gets moved into the cold under the assumption that it's ok because its sealed in its case. Then moisture condenses and it's entombed like that for as long as it remains cold.

An issue I can see is that condensation forms and finds its way into the timber through cracks in the finish, pickup routs and screw holes etc. It wouldn't be much, but a repeated cycle could present serious problems. In particular, timber has a moisture hysteresis in that it tales longer to remove moisture than it does to absorb so we get a ratcheting dampness happening over time that goes unnoticed.

A partial answer could be to house an instrument in a breathable case. I saw Redd Volkaert with a beautiful leather bag - like saddle leather. I guess that would breathe nicely. Maybe there are special cases that have a micro-porous barrier or something. GoreTex case, anyone?

Most people are fighting the opposite problem with guitars drying out too much in centrally heated homes, along with skin conditions and allergies affecting the players.

Hey, don't think I was trying to prove you wrong, just trying to re-orient my own flat-earth model to get a better understanding myself and put some more pieces in the jigsaw puzzle!

[cbarrow7625]

I guess there is an opportunity in there for the case manufacturers. I assume that their top priority is to protect equipment from external mechanical damage, not the kind caused by corrosion and condensation on wood. I thought that the temperature swinging enough to actually cause condensation would be fairly rare, but I was just thinking about home storage. I'm sure the example you gave happens many, many thousands of times throughout the winter worldwide. I wonder if road musicians have been suffering from "mysterious" corrosion problems, pickups breaking down and tone changes from soggy wood forever and have just put up with it quietly because there was seemingly no good explanation for it? Although, I can't imagine every road case is air tight enough to casue these problems but obviously some of them are. Good stuff Mick. Thanks.