Gig Bag Lining Etching into Lacquer Finish

[Crazy4Tbone86]

Hi Everyone,

I have a Holton Tr-256 (.547-.559 dual bore with screw bell) that Todd Clontz converted to a modular bell back in 1996. This was back before I learned to do repair and custom work (it was actually one of the projects that inspired me to learn the skills). Since the screw-rim case is so narrow, the removable F-attachment section has been stored for 25 years in an early 1990s Bach trumpet soft gig bag. The actually bag is in the photo below.

It is a wonderful instrument and I usually play the horn a few times every year, but I rarely use the F-attachment section. I believe the last time I used the F-attachment was in late 2018. Since I know that the F-section might not see frequent use, I always swab the inside tubes and vacuum dry the inside plus thoroughly wipe down the outside tubing before putting it in storage. I even give it a chemical cleaning if I see a trace of lime or mineral deposits in the tubing. The F-section has remained in mint condition for all of these years.

Last night, I took the F-section out and was horrified to see that the sections of tubing that had firm contact with the inside polymer lining had etching marks in the pattern of the lining. It was only the sections that FIRM CONTACT with the lining on the bottom and on one side. The etching was quite pronounced....it went through the lacquer and into the metal a little bit. Today, I was able to buff those sections and relacquer them and the F-section looks great again. I plan to store it with a double layer of T-shirt cotton wrapped around it from this point forward.

I found this to be very peculiar because the F-section has been stored in the same gig bag in the SAME POSITION in the SAME PLACE in the SAME ROOM with the SAME HUMIDITY/TEMPERATURE for 25 years. Why would there be no trace of a chemical reaction for 22-23 years and then suddenly something becomes corrosive. Any chemists or polymer scientists out there who can explain this?

https://trombonechat.com/download/file. ... w&id=10199

[Burgerbob]

I had a similar vintage Bach trombone gig bag for a moment, got it for free with something. Neat bag, I was going to use it for storage... but it immediately marked up something I had in it, and was shedding foam like there was no tomorrow. I had to toss it. I wouldn't be surprised if the foam in those had a certain shelf life and it was recently reached.

[Doug Elliott]

Everything has a shelf life. Manmade materials break down into other chemicals.

[BGuttman]

Could depend on what the blowing agent for the foam was. Modern foams often use carbon dioxide, but in the past foams were created by chemical reaction. I don't know exactly which reactants were used but I think there may have been one that degraded to hydrogen chloride, which would definitely affect brass (though not necessarily lacquer).

I had a cheap gig bag that shed a sticky foam onto whatever I put in it. Had to sideline the thing.

[Matt K]

What's the expected "shelf life" of lacquer assuming perfect conditions (whatever that may be)? I don't know if I ever recall a 20+ year old horn having totally intact lacquer but most horns see more attention than that F attachment does.

[BGuttman]

What's the expected "shelf life" of lacquer assuming perfect conditions (whatever that may be)? I don't know if I ever recall a 20+ year old horn having totally intact lacquer but most horns see more attention than that F attachment does.

An epoxy lacquer like King or LustreConn will have an almost indefinite shelf life provided it was properly cured.

Cellulose lacquers, especially cellulose nitrate, can degrade over time. Still, old cellulose lacquered horns in my possession haven't degraded like Crazy describes.

There is the possibility that the lacquer and the foam had a chemical reaction, but I don't know enough about the materials to hazard a guess what it was.

[Crazy4Tbone86]

Most comments so far have been about the foam. The foam in this gig bag (under the lining) shows no signs of deterioration. It is very soft and appears to be as malleable as the first day I owned the gig bag. I have had gig bags with foam padding that aged, became rigged and broke apart like peanut brittle.....this is not one of those.

I am wondering if there is something in the polyester mesh that has degraded. Of course, the foam padding could be the culprit because it is has contact with the lacquered parts through the mesh. Maybe that is the point that some of you are making?!?

Another interesting observation: The inside tuning slide leg, which has no lacquer, had very firm contact with the mesh/foam and did not have any of the etching. This is definitely something reacting with the lacquer.

[Matt K]

It almost sounds like maybe something hit your bag or something. Maybe something was dropped on it since the last time you opened it and it happened to be at the wrong spot at the wrong time? I might also be misunderstanding what the aesthetic damage was

[Crazy4Tbone86]

The gig bag (with F-attachment inside) has been stored in a little five-inch wide nook in between two areas of drywall in my basement closet. I have been bewildered as to how they installed that drywall for years…….the contractors probably used screws on one side and liquid nails on the other. Anyway, it would be nearly impossible for anything to fall on it. Actually, if a tornado were to rip through my neighborhood, the gig bag would probably remain intact because it sits in the safest spot in my entire house!

I’m thinking that one of the man-made materials in the mesh or foam had a chemical reaction with the cellulose lacquer. I have already removed the etched lacquer, buffed the affected parts and relacquered it. It has cured for three days and I just put it back in the gig bag with two layers of cotton material (t-shirts) wrapped around it. It looks pretty good and is back home in the nook. I’m crossing my fingers that the cotton barrier will prevent any further etching. Only time will tell!

[BaritoneJack]

The trouble is, as I see it, that you've got three complex chemical compounds in the mix - the foam, the lining and the lacquer - and the only one you can be sure of as far as the constituents are concerned is the lacquer you applied yourself; the other two are complete unknowns. As others have said, above, many complex compounds start to break down after a certain length of time, turning into a mix of various elements and different compounds - and only an industrial chemist could analyse them all and work out how any of the degraded products might interact with your lacquer.

I'm just happy for you that it only attacked the lacquer, and not the brass. I had a Selmer student trombone a few years back which the previous owner had left in an attic for several years. The lacquer had developed a mass of hair-line cracks, the brass had started to corrode along the cracks, but then the corrosion had eaten sideways under the lacquer - so I had to strip the about half the lacquer off it in order to reach all the corrosion! Just my luck that the only paint stripper which would have dealt with that particular lacquer is now only available to professionals over here - so it was down to really hot water, nylon pot-scourers, and hours of scrubbing followed by a lot of polishing
(the cost of having it done by a pro instrument repairer would have been far more than the instrument was worth)

With best regards,
Jack