I've seen this a couple of times before, only on Yamaha pianos (not old ones). It had no apparent effect on the tone. I'm digging back into my memory now, but I seem to recall being told that if the piano had been subjected to cold and then brought into a warmer place, some light condensation might have occurred, which got "trapped" under the damper felts just long enough to discolour the bass strings where the dampers contact them. But that doesn't really explain the discolouration where the hammers strike the bass strings. I'm more inclined to believe that the damper and hammer felts absorbed some kind of gas, held it against the strings long enough to cause a reaction with the copper, and then perhaps dispersed it back into the air (or not). The fact that I've only seen this phenomenon in Yamaha pianos suggests to me that the offending substance is something which is sometimes present in their factory. Just my two cents, Albert --- On Mon, 10/19/09, Rob Mitchell <tpa2sfr at pacbell.net> wrote: From: Rob Mitchell <tpa2sfr at pacbell.net> Subject: [pianotech] U1 - stained bass strings To: pianotech at ptg.org Received: Monday, October 19, 2009, 6:31 PM I've been working with Yamaha on this, but the best we've come up with is that some sort of atmospheric contaminant is attacking the strings. Thought I would try this group to see if anyone has seen the problem. This is on a 4 year old Yamaha U1. As you can (hopefully) see from the pictures, this is a very unusual phenomena. It looks to be some kind of ink or marker in some very odd places. It occurs on ALL the wound bass strings under the damper felts and at the hammer strike points. For the damper felts, the stain is exactly at the contact point between the felts and strings. For the monochords, the stain wraps around the string. For the bi-chords, the stain is between the strings from the wedge. It's as if someone used ink-soaked dampers and hammers to check for damper contact and strike point. (The hammers and dampers themselves on this piano are normal and show no signs of the stain). The stain is not just on the surface of the coils -- it seems to be all the way into the grooves. Furthermore, both the L and R strings on B1 (as well as some other strings) have the markings smeared from the dampers almost up to the tuning pins. And there is an every-fourth-string marking again closer to the tuning pins. All the strings look completely normal and free of the markings below the dampers. I tried some fine emery paper on a B1 string and the marks seemed to scrape off fairly easily. I didn't want to try anything more aggressive like alcohol, wire brushing or steel wool. The customer's concern is that at a minimum, this diminishes the resale value of her piano and at worst, might be something that would accelerate string wear/breakage. Anyone seen this before? Rob Mitchell Piano Service (415) 994-1030 www.mitchellpianoservice.com __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20091021/4c6affa4/attachment-0001.htm>
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