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[BKARTS] More on isopropanol question



An azeotrope is a "a mixture of two liquids that has a
constant boiling point and composition throughout
distillation". In our case the water in the mixture is
not somehow magically locked away so as to no longer
affect the rotted leather as water does.
And so I want to ask, which is it? Does your "gut"
tell you that 70% purity (the rubbing alcohol off the
shelf) is good enough as per Wright? Why not 60%? Must
it be in the 80-90% range? And by the by how are you
measuring your solutions? What tosh!
Yes, as many previously noted in this thread, alcohols
absorb water when exposed to the air. This is perhaps
the chief reason we are warned not to leave our
bottles of nor our Klucel solutions sitting about
uncovered.
I take the liberty now of quoting from a users sheet
on Cellugel:
"however, a little 100% isopropanol may be used for
thinning. Water should never be used, as it will cause
staining and blackening of (decayed) leather
surfaces". My interpolation.
As this staining is absolutely irreversible it would,
I think, be advisable to follow the advice of our more
experienced conservators and not rely upon our own
individual gut feelings however well intentioned.








--- Russ Wiecking - Wood and Metal Craft
<russ@xxxxxxxxxxxxxxxxxxxxx> wrote:

> Wiki does good:  "Isopropyl alcohol [isopropanol]
> forms an azeotrope  
> with water at 87.4% alcohol. It is impossible to
> dehydrate isopropanol  
> further using standard distillation methods. For
> this reason, more  
> expensive means, such as using a desiccant, are
> necessary for  
> production of 100% isopropyl alcohol."
> 
>   I do not know if the azeotrope will affect
> leather, but alcohols are  
> hydrophilic. A bottle of 100%, besides being
> expensive, will drop in  
> percentage when the top is removed, absorbing water
> from the  
> atmosphere. The notion that pure alcohol is needed
> as a solvent for  
> this product seems unrealistic. If the product is
> thinnable with  
> isopropanol, then I expect it contains alcohol,
> probably with a minimum  
> of 12.6% water. A chemist could comment with more
> certainty...If the  
> product works for the the use described, I can only
> assume that the  
> azeotrope and/or small quantities of water are not
> deleterious and some  
> thinning with "fresh" alcohol at 80-90% would be
> acceptable.





 
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