Take a bit of pen flush to it.....what goes away, goes away. What stays is going to be mostly hidden by what every ink you have in it..........and it should still show you if it is filled or not.
I'd not go all AR on trying to make an old pen window look new pen clear..........had you wanted that 'really', you could have paid $$ NOS prices for a never inked pen............that might have ambered by sitting anyway.
Those 'dark' ink windows, will show you if you are inked or not easier than the stripped Pelikans (green or tortoise) that have to be held up to the light to see if it's time to refill.
Until this post, I'd not paid much attention to my old '52-54 only made Deluxe MB234 1/2 KOB semi-flex pen's somewhat ambered window. It's an old pen. The ink window is a tad ambered....so what! I can see clearly if I need ink or not...............I need ink..............or to clean it out and put it away.
Red ink is a no no for ink windows................sigh, Purple needs to be cleaned out after every load....in purple is not all that good for ink windows either. One can live with out red ink............that is harder to do with purple. I could see doing a pen flush after every load of Purple ink....just to be safe.
Edited by Bo Bo Olson, 20 May 2017 - 11:01.
German vintage '50-70 semi-flex stubs and those in oblique give the real thing in On Demand line variation. Modern Oblique is a waste of money for a shadow of line variation. Being too lazy to Hunt for affordable vintage oblique pens, lets you 'hunt' for line variation instead of having it.
www.nibs.com/blog/nibster-writes/nibs-germany & https://www.peter-bo...cts/nib-systems,
The cheapest lessons are from those who learned expensive lessons. Ignorance is best for learning expensive lessons.