Re: Scratch resistance of glass


"NoSpam" <NoSpam@xxxxxxxxxxx> wrote in message
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"Kevin Cunningham" <smskjc@xxxxxxxxxxxxxx> wrote in message
news:8a4c0c59-c700-429a-9b7c-0e242ced2b09@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Jul 19, 11:23 am, "NoSpam" <NoS...@xxxxxxxxxxx> wrote:
Hello Group,

I have a question to which some of you may know the answer.

Does glass with antireflection coating provide greater resistance
to scratching than pure glass?

Which of the following two glasses is more scratch resistant:
BK7 or B270?

Thanks for any replies.
GR.

The anti-reflective coating is different from glass, it helps the
light transition from one low refractive index to another higher one.
Most coatings are harder than the glass it sits on. Now thats most.
Check the web sites of glass manufacturers like Corning, they will
list all the characteristics of each glass they make to mind numbing
standards.

Kevin Cunningham
SMS

Hello Group,

Here is a sequence of hardness of MgF2, B270 glass and
BK& glass. It is measured by Knoop's hardness which may
be a measure of scratch resistance of optics in everyday
use.

The sequence in increasing order of scratch resistance is
as follows:

MgF2: Knoop 415
(http://www.crystran.co.uk/products.asp?productid=241)
(http://www.reade.com/Products/Fluorides/magnesium_fluoride.html)

B270: Knoop 542
(http://www.uqgoptics.com/pdf/Schott%20B270%20Superwite.pdf)

BK7: Knoop 610
(http://www.mellesgriot.com/products/optics/mp_3_1.htm)

It appears that, contrary to intuition, MgF2 coating is
relatively soft.

GR.

OK, but then the perfectly well-intentioned (and as I've heard before)
advice of Kevin about the added resistance of coatings must be
reassessed. What's up with that?


.

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