On 08/07/2019 12:46, David Hill wrote:
On 08/07/2019 11:58, Chris Hogg wrote:
On Mon, 08 Jul 2019 10:49:56 +0100, Stephen
wrote:

On Tue, 18 Jun 2019 13:38:35 +0100, Jeff Layman
wrote:

My understanding is that it is due to old glass having many
micro-cracks
and scratches which weaken it and assist in crack propagation
throughout
the glass once it starts. Modern glass (and more expensive glass than
the "agricultural" grade glass often used for greenhouses) has a
surface
treatment to inhibit the production of these microcracks and scratches
over time. So toughened or tempered glass is much less likely to become
brittle.

Hello,

So to update: the galvanised clips arrived but looked a lot bigger. I
measured the "legs" but both the stainless steel and galvanised ones
are 30mm or 1.25" long. The difference is that the legs are at a 45
degree angle on the stainless ones but at a smaller angle on the
galvanised ones, so the galvanised ones have more depth. The
galvanised ones hold the glass perfectly because the legs are "longer"
and under more tension that the stainless ones.

The glass was stored against my garage wall and it has got wet in the
rain. I've noticed that the glass has a white discolouration in places
that I can't seem to clean off. I'm not sure what this is? Perhaps it
is the micro-cracks you talked about, either refracting light or
perhaps something has got into them?

Sheets of glass that are stacked together and get wet can be very
difficult to separate, due to surface tension of the water film
between them holding the panes together. Prize them apart only very
gently or you'll break them, or slide them apart.

The white discolouration is possibly salts that have leached out of
the glass and then redeposited onto the surfaces. You sometimes see a
white deposit on the enclosed surfaces of double-glazing panels that
have failed and moisture has eventually got in, and they've not been
replaced for a long time. Not sure what will shift it - possibly a
very mildly abrasive bath cleaner or similar. It probably doesn't
matter too much anyway for a greenhouse.

Surface hydration damage. You can get irridescent surface layers in
glass which has been buried in soil for a while. You may be able to
polish it out but it isn't worth the effort.
To seperatr the sheets a VERY thin bladed knife is the best way. dont
force them or they will break.

I favour sliding them, but a thin blade will help lift them. It is
definitely something to wear stout gloves handling greenhouse glass.

Eye protection isn't a bad idea either - toughened glass can detonate
into copious 3mm glass grit when or if a scratch gets deep enough.

--
Regards,
Martin Brown