[7453K]

lye etches glass correct? in a water solution thats say 50% lye 50% water, how fast would it etch glass? like how long would it take until the glass is visibly frosty looking?
and i know i could probably get this in a hardware store, but in cleaners do any of them have it pure enoguh to work? like without too many fillers and other stuff.

[Borek]

There many different types of glass, so you will have to check experimentally. Although I don't think lye will be strong enough.

[Arkcon]

Etching glass with base will be a slow process, and like Borek: says, will depend on the type of glass.  The typical soda-lime glass used to make bottles used to ship soft drinks, or glass tumblers, used to store grape jelly, then reused as drinking glasses at home, can contain additives that make them a bit more resistant to base, on general manufacturing principals.  This is compared to real low lime content soda lime glass, meant purely for decorative purposes, and ease of hand blowing, for example, buy some beginner art students.  But real sparkly glass will contain lead salts, which will also defend the glass against attack.  So I really don't know.  I do know you'll have a hard time attacking borosilicate glass -- the Pryex or Tempax brands of heat resistant glass.

OK, here's the way to try it.  Say you've got some glass, maybe a square of glass from a picture frame shop, or a glass tumbler.  You coat it with paraffin wax, and draw a little scene.  And you want to frost the glass, where the scene's been cut away from the wax, right.  Get some horticultural lime -- it's CaO, calcium oxide.  Get it wet, and it forms calcium hydroxide -- CaOH.  Calcium hydroxide is, in fact, a very strong base -- so wear gloves, and watch where this stuff sprays about and splashes.  It's just that, CaO and CaOH are very slightly soluble in water, so there's less active at a time than with NaOH -- but industrially, if you're consuming it as fast as it's made, it is considered a strong base.

So smear a moist paste of CaO, and keep it damp.  As the reaction uses it up, there'll be more to use, already there.  And check it, after a couple of weeks, or months.  These are experiments.  Once you've figured out the time it takes to get the effect you want -- publish it.  You probably won't make the major chemical journals, but we'd like to have your results here, for the next person with the question.  Or post the results online, with pics, on your webpage.

[7453K]

where could i find calcium oxide? and am i correct that hydroflouric acid IS the ONLY acid taht eats away at glass? im talking like window glass, normal stuff.

[Arkcon]

Calcium oxide is called quick or slaked lime, and is sold as a garden supply everywhere.  It is used to make soil more alkaline, and as a source of calcium for proper plant growth.  It is a white powder, that when moist, becomes basic.  Note that your skin, your eyes, and the inside of your nose and mouth are usually moist too, so watch where this powder flies as you work with it.

FWIW, hydrofluoric acid does not attack silicon dioxide (that's most of what glass is made of.)  It reacts, reversibly, with silicon dioxide, to produce hydrofluorosilic acid, which rapidly attacks silicon dioxide.  That's kind of a bit of trivia, you can spout to look cool.  Most people I know find chemistry trivia cool.*  But try to remember that base and acid are on two different sides of the spectrum.  Sodium hydroxide gradually attacks glass, but you won't easily find it cheaply.  You can get lime anywhere.

*Disclaimer: even the biggest chemistry nerds I know do not consider chemistry trivia cool.

[Borek]

Typo: Ca(OH)₂.

[7453K]

haha chemistry trivia. and yeah i know bases are like the opposite o acids, ph scale blahblah. but lime reacts with glass better than sodium hydroxide?

[Arkcon]

Heh.  Borek:, Usually I do remember to balance the charge.  I got a little caught up in the writing out of chemical names, because items in the hardware store don't usually have the formula written in big type on the package and forgot to check.

7453K:, note that base only slightly frosts glass, and only with long exposure.  You'll have to try it and see.

[DrCMS]

FWIW, hydrofluoric acid does not attack silicon dioxide (that's most of what glass is made of.)  It reacts, reversibly, with silicon dioxide, to produce hydrofluorosilic acid, which rapidly attacks silicon dioxide.

I do not think that is true.
HF reacts with SiO2 to give Hexafluorosilicic acid but the reaction is not reversible.

The Si-F bond is the strongest covalent bond I know of while the Si-O bond is the 2nd strongest.  That is principle behind silicon protected alcohols.

[Arkcon]

Gah.  I knew I should have checked my references before spouting off on this forum.  Yeah, I did have it wrong.  The hexafluorosilicic acid is not reversible.   Third-hand knowledge on chemistry from glassmakers tends, not surprisingly, to be flawed.