In the end the bag was certainly fit for purpose, although I think my presence distracted him and he let his machine get the better of him.  There are a number of unnecessary black stitches near the mouth.

When I explained the delay to my teacher, the first thing he asked was the price I had paid for the bag.
"One hundred and eighty rupees," I said. (About £2.25 sterling)
"Ah," he replied. "You should not have paid more than a hundred rupees for a bag like this."
I immediately thought about the sum I had paid him for the flute.

However, he assured me the bag was a good idea, and not for the reasons I had supposed.  Apparently he had twice been bitten on the lips by insects that had crawled into the warm, damp, dark space inside his flute.  The creatures had taken exception when he put the instrument to his lips to blow and inflicted an injury that made it impossible to play for a couple of days, such was the swelling of his lip. This is  not a problem I have ever experienced in the UK.

And then we went up the rickety stairs to the covered part of the juice bar and got down to musical business.