Identify glass

[bluc]

Is there a sure fire way to find out a glass type?
I bought some screw on lens sight glass assays from china but the seller doesnt seem to want to answear my questions.
Price I got them for I could replace the glass and seals and still be in front. But was wondering if I could identify it before ditching it. Was thinking of dropping one into boiling water. Would that do the trick? :-B

[prawnz]

Wander into a local glazier , reckon they could help . Chances are most of the glass they import comes from China as well .

[bluc]

Ok cheers

[A&O]

Float glass when cut will leave really sharp edges. Then a fine sand paper is used to smooth the edges. When broken float will break into shards.

Toughened glass usually has nice smooth edges (usually but not always). That is because it starts live as normal float glass, cut to desired sized then is heated to almost melting point then cooled a number of times. The slightly rounded edges comes from sanding the edges before heat treatment, but because the glass gets so hot, the extreme edges do melt making the sides of the glass a lot smoother. This is the fun part, toughened glass takes a bit to break, because what has happened during the heat treatment the outer layer constricts ever so slightly putting the centre of the glass under immense pressure, giving it the strength. Think of it this way, if you stand on a air hose with no air pressure it deforms easily, but add 100psi, not so easy to squish, keep increasing the air pressure and it becomes harder and harder to deform the hose. Same principle for toughened glass. The outer layer of glass has contracted enough to put massive pressure internally. So hit the middle of a toughened pane of glass with a hammer and it bounces off. Hit the edge or use a very fine sharp instrument, you release the internal pressure of the glass by fracturing the outer layer, and the pane will shatter into millions or little pieces. It’s the sudden release of pressure that causes the whole pane to break.

Laminated glass is 2 pieces of float vulcanised together with plastic. You can see when looking side on the line in the glass. Laminate can be toughened.

Borosilicate glass is moulded through high pressure injection into multi piece mounds or is hand blown into shape. You will see casting lines and marks in the glass. It is usually put through a hardening process after the item has been polished to remove casting marks.

So can you tell what is what. Nah not really. A glassier that has been in the trade for a long time might be able to pick it by seeing some subtle tell tale signs, but you don’t really know what it is until you wack it with a hammer.

[scythe]

Cool info.

And to add:
Borosilicate glass will handle the thermal conditions of a still "float" will not, heat treated glass probably wont either.

If you will still be in front i would suggest getting some glass known to be borosilicate, either from 5star or maybe the local glazier might be able to source you some, but i think 5star would be cheaper.

[pat_00]

I'm in the glass industry, and agree with the previous responses.

To test them, put them in the fridge till cold then tip some boiling water over them, then you should know :)

[bluc]

I'm in the glass industry, and agree with the previous responses.

To test them, put them in the fridge till cold then tip some boiling water over them, then you should know :)

Should i get it real cold like freezer or just cold in fridge?

[bluc]

Cool info.

And to add:
Borosilicate glass will handle the thermal conditions of a still "float" will not, heat treated glass probably wont either.

If you will still be in front i would suggest getting some glass known to be borosilicate, either from 5star or maybe the local glazier might be able to source you some, but i think 5star would be cheaper.

I most likely will but an experiment with the existing glass first me thinks :-B

[bluc]

Stuck them straight in the freezer after about 20 mins was nice and cold. While wearing safety specs dropped it into boiling water....zip zero nada no reaction at all.
Left it in the boiling water for 5 mins then dropped it into an ice water bath still no reaction. I did this with all 4 discs. I think They will be fine..I will repeat this again a few times hot cold hot cold to be sure