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dian
04-22-2015, 01:44 PM
did you know a file can scratch glass? really, i looked it up on the mohs scale and its true. i always thought glass was hard, but that explaines all the scrathes on my expensive glasses. a file does scratch it as does a hardened knive blade (beer bottle).

Royldean
04-22-2015, 02:52 PM
check out the youtube vids of people cutting glass with scissors..... under water!

Paul Alciatore
04-22-2015, 03:01 PM
Scratches in glass are not just due to hardness. Glass is quite hard, but it is also brittle. So, a tool steel wheel on a glass cutter can "scratch" it. It does so by applying a lot of pressure in a small area and the glass under it shatters from that pressure.

And a tool steel will likely be harder than glass.

http://www.tedpella.com/company_html/hardness.htm

http://www.yoshikisolutions.com/application-knowledge-base/material-hardness-and-comparison-table

superUnknown
04-22-2015, 06:20 PM
check out the youtube vids of people cutting glass with scissors..... under water!

It's more like nibbling glass under water, but yes, neat chemical process...

oldtiffie
04-22-2015, 06:35 PM
did you know a file can scratch glass? really, i looked it up on the mohs scale and its true. i always thought glass was hard, but that explaines all the scrathes on my expensive glasses. a file does scratch it as does a hardened knive blade (beer bottle).

From the OP's post, I gather that he is talking about the glass/lens in his "glasses" (spectacles).

If that's so I am not surprised as it seems that there are several makes of lenses each with different "toughness" and optical features to suit the wearers requirements.

An ophthalmologist may refer to lenses as "glass" or "plastic" (at least mine does).

He tells me that mine are "tough" and are a lot less likely to break or shatter if hit by a range of objects that may occur in the house, the shed/shop and everyday life.

That seems to be true in my case as I had a flying object in my shop hit fair and square on my one of my spectacle lenses and when the lens did not break or shatter (or even get marked much) it completely ruined (bent and distorted) and broke the frame. I guess they were "safety glasses" for high hazard and industrial grade.

Otherwise use Mohs scale of mineral hardness :

https://www.google.com.au/search?q=google&rls=com.microsoft:en-AU:IE-SearchBox&ie=UTF-8&oe=UTF-8&sourceid=ie7&rlz=1I7IRFC_enAU360&gfe_rd=cr&ei=bSI4VaKCKqTu8wfwioCIBg&gws_rd=ssl#rls=com.microsoft:en-AU:IE-SearchBox&q=hardness+of+glass

oldtiffie
04-22-2015, 07:29 PM
I thought I'd dig a bit deeper for the hardness of spectacles/glasses lenses as Mohs scale did not seem to address it as well as I'd hoped for - so I Goggled it again for a much better result which is quite informative and interesting:

https://www.google.com.au/?gws_rd=ssl#q=spectacles+hardness

Evan
04-22-2015, 07:40 PM
"Glass" is a very generic term referring to nearly anything that is amorphous rather than crystallized and not necessarily transparent. There are very many types of transparent glass with a very wide range of properties, including the apparent hardness. The most common and basic transparent glass as is used in windows is soda-lime glass which is what is added to silicon dioxide to make the glass. Harder and commonly used for scientific instruments and cooking utensils is known as Borosilicate glass which uses boron and silicon dioxide. It is much harder and has a much smaller change in size with temperature. One brand name is Pyrex. Then there are "glasses" made using quartz which is pure silicon dioxide but is also crystalline instead of amorphous.

Many other combinations of elements are possible and they all have varying properties. Eyeglasses can be made from quite a few of these compounds depending on what is required.

Mcostello
04-22-2015, 10:22 PM
A coworker bought glasses with the miracle coating that they showed on TV that would not scratch with steel wool. After a couple of months He noticed scratches on the lenses. Took them back and they discovered that the felt in the case and ear pieces were scratching them when He took them off and put them in their case. Must not have been felt proof!

oldtiffie
04-22-2015, 10:30 PM
In other words - they were not "up to scratch".

https://www.google.com.au/?gws_rd=ssl#q=up+to+scratch+synonym

macona
04-22-2015, 11:28 PM
You use a file to score glass tubing to snap it. Also a steel wheel on a glass cutter to cut sheet glass. I have even cut glass with a bandsaw and amazingly enough it really didn't shorten the life of the blade.

michigan doug
04-23-2015, 07:59 AM
In spectacle lenses, scratch resistance is inversely related to toughness. So, the most impact resistant polymer used in safety glasses is polycarbonate. But it's native scratch resistance is terrible. To compensate for that, various scratch resistant coatings are applied to the softer/tougher lens material.

Dust is a surprisingly effective abrasive on spectacle lenses. So the first rule is NEVER CLEAN YOUR GLASSES DRY.

Further, if you put a few drops of plain dish soap (eg joy, dawn, ivory) on the front and back of the lens and then rinse under hot water, you will barely have to touch the lenses at all. For the last few drops of water, use a microfiber lens cloth and wash that regularly. Your lens life could double or triple.

doug, the eye doctor

BigMike782
04-23-2015, 08:45 AM
doug, the eye doctor
Doug, can you help me with some lenses that make the reflection I see in the mirror less repulsive:D

michigan doug
04-23-2015, 10:09 AM
Those cost extra. A LOT extra.

janvanruth
04-23-2015, 05:43 PM
they score the little flasks that medicine for injection is in with a small file before breaking the top off

jdunmyer
04-23-2015, 07:47 PM
Take a look at the windshield in an older car, especially one that's had a wiper blade loose the rubber "wiper". You'll see all sorts of scratches; glass really isn't all that hard when it comes right down to it.

Weston Bye
04-23-2015, 08:07 PM
Doug, can you help me with some lenses that make the reflection I see in the mirror less repulsive:D

Beer Goggles?

J Tiers
04-23-2015, 09:51 PM
The only coating for plastic lenses that I have had work well is the "Crizal" coating. I have had the other ones flake off in a matter of weeks to 4 or 5 months, even when using only the cleaning solution and cloths supplied by the optometrist. So far the Crizal is holding up well after most of a year.

I don't think the AR qualities of the Crizal are nearly as good as the others, but it does wear well. It's a little hard to tell, because the optometrist insists on polishing the edges of glasses, which always provide a huge amount of glare and moving reflections. I requested it NOT be done last time, and they did it anyway. I had them fix that (dull it down) on the previous pair, but I waited extra long for these due to the lab messing them up, and was tired of not having them.

BigMike782
04-24-2015, 09:04 AM
Beer Goggles?

Those just make me irresistible:rolleyes::D

rowbare
04-27-2015, 11:52 AM
Doug, can you help me with some lenses that make the reflection I see in the mirror less repulsive:D

I take my glasses off for that!

bob

dian
04-27-2015, 01:06 PM
well, i was thinking about testing hardness of steel. for example i conventionally hardened a socket made of ecn35 (14nicr14). a file just toutches it but it doesn scratch the beer bottle. how hard is it? an other test makes me believe around 40 hrc.