Osram 18w SOX lamp 2: status 2

Lamp 2 from my batch after 2 years in service.
The lamp exhibited significant blackening around the electrodes from new so that the electrodes was not clearly visible.
That cleared right up and went white about a year ago but has now started turning brown around the electrodes.
The browning is strongest around the right electrode as that is not in the middle of the arc tube and is quite close to the wall of the tube.
The rest of it is perfectly clear.

Running on no-ignitor Parma gear.