Why Glass is Green Today

[rideforever]

Hi, I was recently getting some quotes for replacement glass for a window and ... well the default glass has a green tint. Lots of my neighbours had double glazing put in and their windows have that green tint. Not sure what the premium is for glass that is not green.
But my windows seem to be the originals from 110 yrs ago and are clear as day.
How is that possible?
What happened to the glass?
Is it that window glass is recycled and has impurities, or is it that a different type of sand is used, or is it that modern glass comes from a different type of process that is "cheaper".
Would be interested if anybody knows the truth (rather than the salestalk).

Salestalk is :
- yeah nobody will notice if everything you see is green,
- glass was always green since the Neolithic period dontchaknow
- blocks harmful "ultra violet" never go outside very bad
- Brexit !!!!
- it's great for the climate on mars
- you can save agrica with green glass
- "you are not a right winger" are you
- it's not green, it's just an illusion
- it's only green when viewed side ways

Cheers

 

[GhostIntMachine]

I know that the presence of iron oxides in glass makes it slightly green when viewed from the edge, but cullet (recycled glass) has always been used in glass making, so I doubt that is a major factor. Pilkingtons used to source sand in West Lancashire up until the 1980s which was supposedly very pure, but these days I believe they mainly import glass, so that may be a factor. Or it could just be that the greener glass has better UV absorbtion or other properties

 

[crank39]

Glass often has a green tint due to the presence of iron impurities, specifically iron oxides in the raw materials used to make the glass — such as sand, soda ash, and limestone.

Iron in the glass absorbs light in the red and blue parts of the spectrum more than in the green part.

This selective absorption allows more green light to pass through, giving the glass a subtle green hue, especially noticeable when looking at the edge of a thick pane.

Low-iron glass (often called "optically clear" or "extra clear") is made with specially purified materials to minimize this green tint

So, that green edge you see on standard glass is nature's trace left by iron.

 

[Scally-Ho]

Green tinge? Not depleted uranium is it

 

[rideforever]

"Low Iron Glass" never existed before 1980 see ngram below.
Something happened then, possibly Pilkington found that it could shove in the face of the ignorant consumers chernobyl glass which it could buy for 10 c on the dollar.
And in order to do that .... whenever a customer said "why is the glass green", they would say:

"is it ?"
"green you say .... glass has always been green since the neolithic era"
"it's only green when you look at it from the side"
"it's i r o n o x i d e "

And other sheer lies that the building industry is about these days.

 

[crank39]

"Low Iron Glass" never existed before 1980

Something happened then

This green tint is not unique to the 1980s, but the perception that glass became "greener" during that time can be attributed to increased Use of Recycled Glass or cullet

In the 1980s, the push for environmental sustainability grew, and recycled glass began to be used more widely in manufacturing.

Recycled glass often contains more iron and other impurities, especially when mixed from various colored sources.

This led to a more noticeable green tint in standard float glass.

 

[GhostIntMachine]

There's one other more local factor you probably aren't taking into consideration - the source of Pilks's sand. Traditionally Pilks used locally sourced sand. In St Helens and across West Lancashire there is a layer of Shirdley Hill Sand sand up to 2.5 metres thick in places, just below the surface soil. That sand, combined with readily available local coal and the proximity to the large conurbation and port of Liverpool made St Helens an excellent location to make glass.

Originally Pilks used this local sand extracted from beneath farmland in West Lancashire by a process known as "sand getting" - where the overburden was removed by an excavator, the sand was then removed and transported to a sand (by narrow gauge industrial or standard gauge rail, overhead ropeway or in later years by lorry), land drains were installed and then the overburden (soil) was replaced. Anyone who drove along the East Lancs Road or Rainford Bypass up until the 1970s would have seen this first hand, although AFAIK the ropeways disappeared in the 60s.



Pilks started to run down the extraction of local sand in the 1970s, but even in 1973 nearly half their sand was locally sourced (140k tons out of a total of 340k tons), the balance at the time coming from Belgium. The better quality local sand was always retained for sheet glass production, but with new methods of sheet glass production (most notably UK5, the first tin-bed float glass plant which came on stream in the late 1970s) it became possible to make a wider range of thicknesses (0.4mm to 25mm as opposed to a maximum of 6mm with the original mercury bed process). From about 1975 local sand was being mixed with Belgian sand for float glass production with Belgian sand being used for sheet (plate) glass produvtion and Fibreglass using sand from Chelford in Cheshire. Local sand getting ceased altogether in the mid-1980s and my understanding is that more imported sand is used these days, especially at the sites outside St Helens

If you are still with me at the end if all that, then the answer us that the type of sand has changed and that the modern glass is made from sandvwith a higher iron oxides content because they now can. It's also worth noting that cullet is often taken in in mixed colours as opposed to separated into clear green and brown as was once the case

And I'd like to thank my uncle who worked for Pilks for many years for the one hour plus ramble we went on this afternoon in order for me to garner the information (he's now in his 80s) plus a bit of on-line research and a bit of digging in some books on geology. So sorry, not Chernobyl glass, nor larger percentage of recycled glass, just a cheaper non-local source of sand with a higher iron content

 

[rideforever]

@GhostIntMachine
Thanks for that.
However that doesn't really explain everything.

Even if they got the sand from Belgium doesn't mean it was any better or worse impurities.
I wonder if they simply found a way to use bottle glass for windows and switched it.

Lots of my neighbours have spent £50,000 on double glazed bays and now stand proudly clucking outside .... but their windows are green. How dumb are people ? Quite dumb imo.
I know I know you only see it from the side and UV is very .... very .... bad for you.

Today they call it "low iron" glass .... but in fact it is just normal glass.
What they try to foist on people is "high iron" glass made in a cheap way.
That's all the usual building trade bare faced lying.

 

[GhostIntMachine]

What they try to foist on people is "high iron" glass made in a cheap way.
That's all the usual building trade bare faced lying.

Not really; it's simply a change in the way the world works. So just where is the building trade lying? Glass is highly energy intensive and also used to be relatively labour intensive - both major cost factors. By using a higher percentage of cullet the energy cost of glass production, together with its' carbon footprint are reduced. And culet has always been used to make glass. Apparently furnace life is also extended, another cost saving.

The vast majority of cullet used in window glass is still the of "virgin waste" type, i.e. trimmings from within the glass works, combined with clean industrial waste (dismantled window unit glass and trimmings, etc from glass merchants and the like). But even then this cullet is only a percentage of the total raw material used, and post consumer cullet is a fraction of the total cullet used. So they aren't making glass 100% from recycled bottles - but so what if they were? It's glass, not sausages

As far as glass being made "in a cheap way", glass has always been made in the cheapest way possible because it is so expensive to produce. When Pilks invented the first mercury float glass process it reduced the price of 6mm window glass considerably, as well as increasing production rate, reducing labour content and improving flatness and consistency. Bit without float glass there could never have been any affordable double glazing. In the 1980s when they started to move over to the current tin float glass process they were able to increase production rates still further, almost completely automate cutting and handling (and so so lower labour costs), and also vary the thickness of glass produced from 0.4mm to 25mm within a run (thus ending the need to cast and roll plate glass amongst other things - 1st generation float glass could only be made in a small range of fixed thicknesses). The newer process was also potentially less environmentally damaging because the float beds now used tin instead of (possibly toxic) mercury previously employed.

Manufacturing has always been about improving efficiency and reducing costs. If we were still making glass the way the were in 1950 your house glazing would be lot more expensive. Then you'd really have something to complain about

As it happens you even see greenish glass in original panes of glass in the window sashes of Georgian and Victorian buildings, installed new. The green tinge seems to vary from district to district which may indicate differing sources of sand at the time and/or production techniques used

 

[rideforever]

@GhostIntMachine
Okay I am not really interested in your political ideas, thanks anyway.
You said earlier that cullet (or recycled glass) has no bearing on the green tint, I am not sure why you are still talking about it.

The question is still unresolved. If some UK glass brought sand in from abroad, did the UK sand run out, was the sand from overseas worse? I don't want a guess.
Perhaps somebody knows the answer, or not.

Clearly there have been improvements to processes, perhaps it was that that facilitated the foisting on the public of green window glass, I don't know but it's a typical action.

Ah .... yes it's not really green is it, only from the side, and only on Wednesday afternoons.
You deserve everything you get in this life.

 

[crank39]

At the end of the day it has been accepted that glass has a green tint because it has iron in it because thats the standard way glass has been made, to the average person it doesn't even become a thought or an issue however for those who are more informed then you can have glass that is clear[er] for a cost.

I'm kind of confused now as I thought the original question was why is glass green - what makes it green?

 

[ronniecabers]

Is it a green tint in the glass you are seeing on your neighbours or the reflection from the metallic coatings used to produce Low e glass ?.... I very much suspect the latter .

 

[crank39]

I was going to mention the Low e tint, I'm red/green colour blind so I don't see those colours the same way as others who have normal vision, I don't see green whilst looking through the glass but can see it when looking at the edge, the only green I see when looking through the glass is when its green anti-sun same as blue/bronze/grey anti-sun glass. To me Low e in hard coat form like Pilkington K or Saint Gobain Eco-logic gives a horrible bluey hue when looking outwards but looking inwards makes net curtains look like the occupants smoke 80 a day and unless I'm matching to existing I always spec a soft coat usually Saint Gobain Planitherm or Planitherm Total + as personal preference over say Pilkington KS, never needed to spec opti clear glass because non of my customers have 1/ asked for it and 2/ it wouldn't match the existing

 

[GhostIntMachine]

I'm kind of confused now as I thought the original question was why is glass green - what makes it green?

Yes. The glass is a bit greener partly because the Belgian sand used nowadays contains more iron oxides, but coatings applied to modern glass also add to the tinting - just like it changed how camera lenses looked back on the 1970s/80s when they moved over to multi-coating lenses

 

[GhostIntMachine]

Okay I am not really interested in your political ideas, thanks anyway.

What politics? WTF are you on?

The question is still unresolved. If some UK glass brought sand in from abroad, did the UK sand run out, was the sand from overseas worse? I don't want a guess.

In effect, yes it did. I did state that. Obviously you don't follow what was being said

Clearly there have been improvements to processes, perhaps it was that that facilitated the foisting on the public of green window glass, I don't know but it's a typical action.

Are you some kind of conspiracy theorist, then? Even in the Victorian period some window glass was actually green when viewed from the edge. Not a lot of people know that

You deserve everything you get in this life

So do you you ignorant, nasty piece of work. Keep taking the medication. I think you need it