# Which is sharper: Steel or Glass? **URL:** \ **Category:** Factual Questions\ **Created:** [October 24, 2005, 2:57pm UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664 "2005-10-24T14:57:38Z")\ **Posts on this page:** 13\ **Page:** 1
**Author:** ![Buccaneer\_Booster](https://avatars.discourse-cdn.com/v4/letter/b/b3f665/32.png) [@Buccaneer\_Booster](https://boards.straightdope.com/u/Buccaneer_Booster)\ **Post date:** [October 24, 2005, 2:57pm UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/1 "2005-10-24T14:57:38Z")
My foolish coworker Phillip and I have come to an impasse in a dispute. He claims that a glass edge is sharper than any steel one. I contend that while glass is sharp, it is not sharper than the sharpest steel blades. Who is right? ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [October 24, 2005, 3:07pm UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/2 "2005-10-24T15:07:16Z")
Obsidian (a type of naturally-occurring volcanic glass) is used to make surgical blades much sharper than can be made with surgical steel, if that helps… Cite: > **[Obsidian](https://en.wikipedia.org/wiki/Obsidian)** > > Obsidian (/ˌɒbˈsɪdiən/; /əb-/) is a naturally occurring volcanic glass formed when lava extruded from a volcano cools rapidly with minimal crystal growth. It is an igneous rock. > Obsidian is produced from felsic lava, rich in the lighter elements such as silicon, oxygen, aluminium, sodium, and potassium. It is commonly found within the margins of rhyolitic lava flows known as obsidian flows. These flows have a high content of silica, giving them a high viscosity. The high viscosity inhibits diff... ---
**Author:** ![CynicalGabe](https://avatars.discourse-cdn.com/v4/letter/c/3e96dc/32.png) [@CynicalGabe](https://boards.straightdope.com/u/CynicalGabe)\ **Post date:** [October 24, 2005, 3:24pm UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/3 "2005-10-24T15:24:47Z")
This sort of debate can only be settled though the consumption of alcohol and the puffing of chests until one party or the other exclaims: "Oh yeah? Well, watch _this_! ---
**Author:** ![R.P.McMurphy](https://avatars.discourse-cdn.com/v4/letter/r/7993a0/32.png) [@R.P.McMurphy](https://boards.straightdope.com/u/R.P.McMurphy)\ **Post date:** [October 24, 2005, 3:33pm UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/4 "2005-10-24T15:33:07Z")
> [@CynicalGabe](#): > > This sort of debate can only be settled though the consumption of alcohol and the puffing of chests until one party or the other exclaims: > > "Oh yeah? Well, watch _this_! Do I smell a Darwin Award? ---
**Author:** ![scm1001](https://avatars.discourse-cdn.com/v4/letter/s/c4cdca/32.png) [@scm1001](https://boards.straightdope.com/u/scm1001)\ **Post date:** [October 24, 2005, 3:37pm UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/5 "2005-10-24T15:37:06Z")
The sharpness of a blade depends on its hardness, how thin it is at its edge, and its toughness. The toughness counts because many materials are too brittle to make good edges that last, e.g. they break and blunt. For a one off use the main property that counts is its hardness. The trouble with “glass” is that it covers a large amount of materials and could include some ceramics. Glass and steel have similar harnesses, and it is possible to get some steel to scratch glass and vice-versa. However, it is much easier tio generate a good glass edge than a steel edge simply by breaking the glass. Normal glass is too brittle, however in some formulations it can be useful as a coating. Here is an audio discussion on the concept [http://www.bbc.co.uk/radio4/science/thematerialworld.shtml](http://www.bbc.co.uk/radio4/science/thematerialworld.shtml) I would say it was a draw - however it is probably easier to make steel harder than normal soda glass harder. ---
**Author:** ![ryobserver](https://avatars.discourse-cdn.com/v4/letter/r/b2d939/32.png) [@ryobserver](https://boards.straightdope.com/u/ryobserver)\ **Post date:** [October 25, 2005, 12:16am UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/6 "2005-10-25T00:16:39Z")
FWIW, when I took a histology lab course I was taught that glass blades are indeed sharper than steel blades and should be used for cutting finer sections than steel can manage. The next step beyond glass, we were told, was diamond blades, which we as students didn’t get to handle. We also learned a neat, economical trick for making the blades by snapping microscope cover slips. (You can’t buy pre-made glass blades; they don’t hold an edge, so they have to be made right before use.) ---
**Author:** ![Hello\_Again](https://avatars.discourse-cdn.com/v4/letter/h/85e7bf/32.png) [@Hello\_Again](https://boards.straightdope.com/u/Hello_Again)\ **Post date:** [October 25, 2005, 1:55am UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/7 "2005-10-25T01:55:21Z")
Corning Museum of Glass agrees with your pal: [The fact that the edge of a newly chipped flake [of obsidian] is sharper than surgical steel was only discovered in the 1970’s, and it has led to the use of obsidian blades in eye surgery, since the evenness of their cut permits much faster healing.](http://www.cmog.org/index.asp?pageId=765) ---
**Author:** ![Folly](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/folly/32/3219_2.png) [@Folly](https://boards.straightdope.com/u/Folly)\ **Post date:** [October 25, 2005, 3:55am UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/8 "2005-10-25T03:55:21Z")
If your glass swords aren’t sharp enough, simply cart around a nuclear bomb with the trigger switch linked directly to your brain waves. [snow crash](http://en.wikipedia.org/wiki/Snowcrash) ---
**Author:** ![Aserrann](https://avatars.discourse-cdn.com/v4/letter/a/82dd89/32.png) [@Aserrann](https://boards.straightdope.com/u/Aserrann)\ **Post date:** [October 25, 2005, 4:28am UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/9 "2005-10-25T04:28:36Z")
> [@Folly](#): > > If your glass swords aren’t sharp enough, simply cart around a nuclear bomb with the trigger switch linked directly to your brain waves. > > [snow crash](http://en.wikipedia.org/wiki/Snowcrash) Funny someone should mention Snowcrash… i was curious, in a closely related question… how accurate are the knives in that story? For those who have not read, basically one character makes knives by chipping an edge onto plate glass, and they are extremely sharp, but very delicate… ---
**Author:** ![crowmanyclouds](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crowmanyclouds/32/19884_2.png) [@crowmanyclouds](https://boards.straightdope.com/u/crowmanyclouds)\ **Post date:** [October 25, 2005, 4:57am UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/10 "2005-10-25T04:57:30Z")
> [@Aserrann](#): > > For those who have not read, basically one character makes knives by chipping an edge onto plate glass, and they are extremely sharp, but very delicate… Like this [one](http://www.bladegallery.com/knives/knife.asp?knifeid=505&alt=one&pics=big) made of glass from the Hubble Telescope? ---
**Author:** ![Aserrann](https://avatars.discourse-cdn.com/v4/letter/a/82dd89/32.png) [@Aserrann](https://boards.straightdope.com/u/Aserrann)\ **Post date:** [October 25, 2005, 5:08am UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/11 "2005-10-25T05:08:03Z")
er… wow… yes, i think so… i was asking about theory, i didn’t expect anyone actually made them… ---
**Author:** ![crowmanyclouds](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/crowmanyclouds/32/19884_2.png) [@crowmanyclouds](https://boards.straightdope.com/u/crowmanyclouds)\ **Post date:** [October 25, 2005, 5:21am UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/12 "2005-10-25T05:21:27Z")
Google “knapped glass knives”. They even come in pretty colors! 🆒 ---
**Author:** ![Hello\_Again](https://avatars.discourse-cdn.com/v4/letter/h/85e7bf/32.png) [@Hello\_Again](https://boards.straightdope.com/u/Hello_Again)\ **Post date:** [October 25, 2005, 4:11pm UTC](https://boards.straightdope.com/t/which-is-sharper-steel-or-glass/327664/13 "2005-10-25T16:11:25Z")
One of my professors, who was an expert flint knapper, used to buy glass in large colored chunks and give demos to the archaeology classes on making obsidian blades. Very cool!