Glass impurities

[ChrisG]

Comparing water white glass with standard picture glass the latter has a green tinge that I always thought was due to iron impurities. Is this right and if so why green and not a brown or red tinge?

[caro]

I couldn't explain why green and not brown or red, but there's a fascinating article all about light transmission UV etc. especially framing glass here: http://en.wikipedia.org/wiki/Picture_framing_glass
Caroline

[caro]

perhaps the FATG could award a couple hundred CPD points for reading and understanding the article!

[Graysalchemy]

I doubt anyone at the fatG would understand it either.

[Not your average framer]

Is this right and if so why green and not a brown or red tinge?

Compounds containing iron come in quite a range of different colours. The follwing compounds are just a few of them:

Iron oxide (ferric oxide) is the most commonly recognised iron coumpound to be associated with the redish brown colour when in it's FE2O3 molecular form, ferric oxide also occurrs in it's FE2O4 molecular form which is black instead of redish brown.

Iron sulphide (ferric sulphide) is metallic gold in colour and is also known as "fools gold".

Iron Sulphate (ferric sulphate) is yellow in colour,

Iron chloride (ferric chloride) is green in colour when dry, but changes to brown when diluted with water.

Iron silicate (ferric silicate) is also green in colour,

Iron phosphate (ferric phosphate) is also green in colour.

And Iron hexacyanoferrate (ferric hexacyanoferrate) is blue in colour.

Normal glass is produced from silica and soda heated at high temperatures, so my guess is that the green colour in glass is because the iron in the glass is in the form of Iron silicate.