Cleaning Glass with Sodium Hydroxide

Has anyone ever worked with oven cleaner to remove staining from aluminum screens?  It works really well!  Sodium hydroxide has a voracious hunger for certain metals.  It will even eat up soda lime glass in minutes.  At the right temperature and concentration.  Did you also know that restaurants use a product based on this chem to clean the grease off their grills?  Did you know too that it is used at farms to completely liquify dead animals?  Also it is used at 100% concentration in the form of crystals to eat up hair in household drains.  Furthermore it is used in food products. We eat it!  So why not clean with it?

OK.  So I went out and picked up the 100% dry crystals at the hardware store.  It cost me about fifteen bux for sixteen ounces. I had a pizza/sub shop to clean that I was called back into after at least four years.  Use your imagination.  It was bad.  My cleaner was worse.  It ate right through everything.  There were  a few windows that hadn't been touched at all for several years. They looked like they had a dark solar tint on them.  So I needed to scrub a little with 0000 steel wool.  But when I was done that glass was crystal clear.  Of course my skin was black and dried out.  Next time I will use gloves.  Infact let me say this.  Sodium hydroxide will really burn your skin bad.  And you should never let even the smallest amount in your eyes.  So gloves and goggles probably would be best.

In practice I discovered that rather than a teaspoon per gallon I could get away with ONLY  1/8th of a teaspoon per gallon;...or less!  I didn't say a tablespoon.  I said a teaspoon!  And this is for routine cleaning at a pizza/sub shop.  Restoration grease stripping would require more.  Remember to always used rubber gloves too.  Keep your hands dry.  As an interesting additional thought I was wondering about the use of plastic compositional abrasives in connection with more powerful alkaline cleaning chems such as sodium or even potassium hydroxide.  I have written an entire newsletter (The Vision Glass Detailer) on putting together a specialty cleaning formula based on an alkali, a nano colloidal silica, and a hydrophobic silane sealer.  This cleans and seals in one step.  But it is just one variation of the idea of coupling different elements to get superior results.  The idea here would be to add cushioned plastic compositionals to a flat wand to wet and scrub the glass simultaneously.  Do you hear me on this one manufacturers?  I know you have already tried different things.  But you have been off regarding the size of the particles or 'strands' used.

So here are the questions.  Since the technical literature that I have read indicate quite plainly that very strong alkali solutions will etch glass, will a much lighter solution of sodium hydroxide also cause etching?  My thoughts are that it will.  In fact it should cause complete dissolution of the glass surface.  I mean;...check out this video.  http://www.youtube.com/watch?v=nmktRTHL1NA  We need to know if this could be visible or not.  Therefor I suggest performing the two different tests I have developed here for acids.  It is true that water itself is quite capable of etching glass.  But under conditions other than routine cleaning.  So when testing cleaning/restoration solutions of sodium hydroxide we should stay with the concentrations used in each.  It is also obvious if we use much higher concentrations at much higher temperatures, than we absolutely will etch glass. 

When I tested the different acids used in so called commercial restoration products (none will be mentioned by brand name in this blog), I tested them at the concentration that is suggested they be used at.  I also tested them at the temperature they would be routinely used at.  Time is also a condition.  Certain acids will show etching in as little as thirty seconds.  To create visible distortions of the surface I did wait thirty minutes.  However there are times in practice when this amount of time could be a factor.  Such as when the solution puddles at the bottom of the window and remains there since it might be an overcast cool day.  It is also true that the glass might be dark and very hot from the sun.  Both the composition of the glass and the temperature could easily contribute to the visual effects of such acids (etchants).

There are other questions that should be answered.  Such as the problem of the yellowing of white vinyl window frames and vinyl siding.  Oven cleaner will yellow out white vinyl in seconds.  Especially on a hot day.  It is based on a 4% solution.  At what concentration is a sodium hydroxide routine cleaning solution safe to use around white vinyl?  To answer this I might heat up some water to about 180 degrees F.  Put in a certain amount of crystals.  Mix it up.  Then do the dip.  Dunk a strip of white vinyl used on window frames.  Leave it in there for at least five minutes.  Remove and inspect in bright sunlight.

So.  I certainly don't write for the ASTM.  None of us are scientists.  We are Window Cleaners.  Nonetheless I do believe we should become accustomed to testing the different products and chemicals we use routinely in our work.  Since we are professionals!

Written by Henry Grover Jr

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