Double glazing and aluminium as a frame material.
Quite a subject this, because since the start of aluminium as a double glazing frame material there have been so many advances.
To begin with:
Aluminium, as a double glazed window or door frame material, was extruded in some fairly simple single chambered profiles. This was pretty basic, anodised to 8 microns, and 'battleship grey', with a 6mm air gap between the glass. When the silver grey aluminium windows first started appearing along with their expensive looking hardwood frames, one or two houses at a time here and there, these home owners were quite often the envy of the neighbourhood, and were making little short of a fashion statement in those days!
I remember it well - and what a marketing coup for the outfit that tells us that you only change your windows once, so 'fit the best'. What did the back room marketing boys dream up: they contacted all their old customers and with the message: we will take back in part exchange the secondary glazing we did for you for our new replacement windows. An absolute master stroke!!!
Since then of course the myth that you only ever fit new windows once has been well and truly dispelled with all those old silver battleship grey aluminium windows now being replaced again. They were only ever in the secondary glazing market at one time, then started making complete new replacement windows.
Off on a tangent, a bit like Ronnie Corbett - sorry - but that reminds me - do you remember Ted Moult, the feather and the helicopter - where have all the years gone??? And I liked watching Barry Bucknell and his D.I.Y. programme. If you don't know what on earth I am talking about - ask your Dad!
The anodising depth for silver-grey was increased to 25 microns, as I believe it still to be today. This finish was also done in 'gold' and brown, for the domestic market. The 'gold' finish always had a problem with shade consistency, which would vary depending on how long it was in the anodising process. The other main finish is Polyester powder coating 'painted'. As far as I understand it, this process is called 'electophoretic' where the metal has an electrical current running through it and the powder is 'attracted' to the metal in a uniform layer some 75 microns thick, when it is then heated and liquefied, and then baked on.
Metal is inherently cold to the touch, and as an insulator nothing like wood (or plastic), and something had to be done about the aluminium frames 'sweating'. Along come "Thermal Clad" and "Thermal Break", the latter of which won the day, and is the most favoured today, although thermal clad is still made, as far as I know. Thermal Clad fell really by the wayside after a major scandal erupted with a national window replacement company about fungus etc growing between the interior plastic cladding and the main aluminium frames.
Thermal break describes a frame where the outdoors and the indoors of the frame are broken thermally. This means that the indoors can be warm as toast and the outdoors freezing, but the two are disconnected thermally. The name of the process which achieves this is called 'cut and fill', where a chamber in the middle is filled with an insulator, and it works very well too.
Double glazing that looks just like PVC-U, but in fact it is the latest generation of high security Aluminium windows, direct fix without a wooden sub-frame. Excellent, but expect to pay a lot more than for PVC-U, say + 25%.
For double glazing aluminium still has a justifiable place in today's market, most notably with recent 'composite' innovations, where the aluminium is on the outside, and you have the traditional wood inside, for aesthetics. Also, there are 'direct fix' aluminium window and door systems now, which remove the need for the traditional hardwood sub-frame. Expect to put your hand fairly deeply into your pocket for either of these though, but some would agree the extra was worth it, and I might just side with them under certain circumstances, and especially if I were in the "if you have to ask the price-you can't afford it" bracket.
Tip on cleaning silver aluminium: use 'Solvol Autosol' aluminium polish, from motor accessory shops.
Tip on repairing damaged white aluminium: I use 'Humbrol' white as a touch-up paint, it's just right.