How to remove coatings from Flash tubes?

[Mark Jones]

anyone know how to strip the yellowish coating off of a monolight flash tube so it is clear?

any xeon flashes are NOT uv coated? I have some chinese ones I should probabaly test.

[enricosavazzi]

There are two ways to industrially lower the UV emission of a xenon flash tube. One is to coat the tube exterior, for example by vacuum-sputtering it with gold. The other is by adding UV-absorbing stable pigments to the glass formulation. In the latter case, there is no practical way to remove the UV-absorbing chemicals. So what you should find out first is whether the tube you want to modify is coated or built with UV-absorbing glass.

 

Xenon tubes for UVC irradiation are built with quartz, but photographic tubes are more frequently built with a glass similar to Pyrex, which blocks most UVC and part of UVB in any case. So removing the coating from a commercial flash tube will allow it to emit UVA, but likely not much UVB and no UVC.

 

My first thought to remove gold coatings would be a chemical treatment, for example:

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1475-4983.2007.00718.x

 

I know that others have removed coatings from lenses and flash tubes by polishing it off (which is a gentler way to describe mechanical abrasion), but this most likely creates microscopic scratches in the glass surface that is very likely to weaken it and increases the risk of explosion of the tube during use.

[enricosavazzi]

Also, some studio flash manufacturers offer non-coated tubes as replacement parts for their products. I know that Bowens did, and that is how I converted my Bowens units. However, Bowens went broke and closed their production lines a few years ago. In addition, some of the Bowens units use three-electrode tubes that require special electronics. I believe that most studio units use two-electrode tubes (plus the external trigger wire).

 

Probably some other brands also offer non-coated tubes, but I have had no reason to seek this information.

 

EDIT: It seems that Bowens is back in business as a brand, but I don't know where their new products are made. Perhaps rebranded units from China:

https://www.wexphotovideo.com/shops/bowens/

[Mark Jones]

interesting, only want to use uva, thank you.

[Shane]

I know that others have removed coatings from lenses and flash tubes by polishing it off (which is a gentler way to describe mechanical abrasion), but this most likely creates microscopic scratches in the glass surface that is very likely to weaken it and increases the risk of explosion of the tube during use.

 

15 years later and still not a problem. You could always use aqua regia if you are that worried but probably less dangerous polishing it off.

 

Used (pre worn) 1000 grit and I used to use 12 micron paper. I have done many of these and it is interesting to note that, even for the same manufacturer, some are stubborn to remove and some literally come off just by looking at them. Possibly due to insufficient glass preparation prior to coating.