Great use for wood ash - glassware restoration

We have a bunch of simple pint glasses and smaller juice glasses that have developed a hazy bluish/white surface after years of use, so I thought before replacing them, I'd see if I could clean them up a bit. Some of the damage was done shortly after we put in a water softener years ago and didn't reduce our detergent enough, but they've gotten progressively worse over the years.

I remember in school, chemists always had base baths with potassium hydroxide that did a good job of cleaning up glassware if it was allowed to soak for an extended period of time, so I figured I'd give it a shot. As I recall, it slowly etches the glass surface. I poured a few gallons of water into a large rubbermaid container and added a load of cool wood ashes from the stove, and then dropped three glasses into the mixture.

After a couple of days, I didn't see any real improvement, but after a couple of weeks, they look great! It doesn't take out scratches, but the glass is crystal clear as good as it was when new. The water has a very slippery feel to it so it's obviously got a pretty high concentration of base in it - rinsed immediately after pulling the glass out.

I'll probably run all this through a homemade straw/cloth filter to separate the ash particles and then continue on with more batches of glassware. I've read that some people would use such solutions to eventually make soap - when I'm done, I might try concentrating it outside in the sun to see how much KOH I can recover. Anyone know just how much can be recovered per pound of ash? I'm sure we have a true laboratory chemist on here somewhere...

-Colin

NewtownPA said:

Thanks for the tip! I'd like to try it too, but "a few weeks" is a long time.

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Yes, indeed... I want to improve the turnaround time. I'm cleaning in batches at the moment - it'll take me some time to get them all done. But sure beats throwing them out and getting new glasses!

I suspect it depends a lot on how much you concentrate the solution. While this solution sat in my garage, about half the water evaporated, so now it's a lot stronger. I put a new batch of glasses in last night - I'll check them regularly to see how long they take - perhaps they will be faster. I figured I'd start fairly dilute and see how it did, and concentrate it until I get to something like a 1-2 day process. I should try taking a picture of the before/after to see if I can show the improvement. I have lots more ash as well so I could probably speed it along by extracting more KOH.

In case anyone wants to try, right now, my mix is about half a paper grocery bag of ash to about 5 gallons of water. Real scientific

-Colin

NewtownPA said:

Do you (or anyone) know how it works chemically? Does it eat away at the glass, or simply dissolve the cloudy stuff on the surface?

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I checked this online to be sure - the potassium hydroxide does indeed etch glass. It will depend somewhat on the strength of the solution and it is really at a very miniscule level. In fact, detergents and rinse agents also etch glass but the process in the dishwasher, coupled with the dry cycle, isn't quite so uniform. This leads to a lot of the haze. And of course some residues just don't come off the glass that easily. So by fully soaking it in a bath, you more or less eat away a microscopic layer of the glass surface in a way that takes away surface impurities and leaves a crystal clear smooth surface.

The other way you can tell it's not etching much is that fine scratches remain even after my two week soak, so it's not etching all that deeply into the glass to smooth them out.

-Colin