I moved into a house that has a light fitting that has been made out of an old food 'tin' can.

The light hadn't worked since moving in. On trying to remove it the glass of the bulb pulled straight out into my hand. There is a white powder on the bulb and also the wire towards the bulb.

It also looks in a structure like mould or mildew, as the 'white' is also up the wire and on the beam that the light lead is hanging from.

What is the powder? Is it dangerous, as in corrosive to other materials as it fell onto the floor and myself? Or is it possible that it is more a mould?

Where the bulb was

What the cord was hanging from

Looking at top you can see holes where mould/chalky structure has developed. Chalkiness on cord.


IMO this might be tungsten(VI) oxide, $\ce{WO3}$, which is fairly non-toxic, unless you consume it spoonwise.

From the look of this DIY setup I would doubt the quality of the light bulb itself was superb, and most likely one wouldn't use a fancy lamp anyway. So, the glass enclosure could be breached and some point, and the inner inert atmosphere (Argon/Nitrogen) was substituted with air. When hot tungsten filament oxidizes, it produces tungsten oxides which evaporates/scatters from the filament as white smoke:

$$\ce{2W + 3O2 -> 2WO3}$$

Actually, bulky $\ce{WO3}$ is yellow, but being dispersed in a form of tiny crystals, tugsten(IV) oxide has pale-yellow or white color depending on the fraction.

Anyway, I would get rid of this can enclosure and buy a decent light source, mainly from an aesthetic point of view.

P. S. Here is a funky experiment showing what could happen in your case: https://www.thenakedscientists.com/get-naked/experiments/light-bulbs-liquid-nitrogen

  • $\begingroup$ If it is tungsten(VI) oxide, WO3, and fairly non-toxic. Are there any corrosive properties or further damage that could ensue from dispersed crystals? Much shook loose freely whilst getting rid of the light set-up. $\endgroup$ – user46732 Jun 22 '17 at 1:27
  • $\begingroup$ Well, $\ce{WO3}$ is considered to be mild irritant, for more info you can check MSDS (e.g. here: sciencelab.com/msds.php?msdsId=9925359). I think if you don't try to eat or inhale on purpose stuff from that can you are gonna be fine. Damaged fluorescent lamp would be a totally different story due to potential mercury contamination, but conventional filament lamps are pretty much safe from this point of view. $\endgroup$ – andselisk Jun 22 '17 at 2:20
  • $\begingroup$ I must add though that I don't have medical degree, therefore I can only speak for what I know is applicable to an average healthy person. If you have specific allergies, or any other pathologies, or unsure how this could influence your well-being, please contact your doctor directly. When it comes to health issues, internet might not be the best place to stumble upon. $\endgroup$ – andselisk Jun 22 '17 at 2:31
  • $\begingroup$ @andyselisk Correct. I was not so much questioning harm to health, but the possibility of damage to other materials crystals have come in contact with (fabric, nylon etc). $\endgroup$ – user46732 Jun 22 '17 at 2:55
  • $\begingroup$ I wouldn't expect more damage from tungsten oxide than from mud or dust. $\endgroup$ – andselisk Jun 22 '17 at 3:14

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