[Otari5050]

Hi folks, got a nice KT88 tube (NOS) which has an unusual white deposit on the inside of the glass.

At first I thought it had gone to air, but the getter is perfect and a check on an AVO MK4 shows it's in perfect health, no gas at all.

Sorry the photo isn't the best but it's hard to get close.
You can see where it's white from the base up, but then goes clear before the bend in the glass.

I've never seen this before in a tube.
I'd like to get others' thoughts on this.