Replies

1. 
   byhammerandhand | Sep 01, 2005 05:52am | #1

   see FWW 151 article by Jeff Jewitt. Below are his comments on shellac solvents:

   Thinner /Drying time /Comments
   For shellac:
   Pure gum spirit turpentine /Slow /Retarder: add one teaspoon to 4 oz liquid shellac
   Isobutanol /Medium slow /Retarder, difficult to find, strong odor
   Isopropanol /Medium slow /Retarder for brushing. May be sold as gas line antifreeze (check label)
   Denatured alcohol /Medium fast /Main solvent
   Methanol /Very fast /Speeds up drying time. Difficult to find except for professional finishers

   
   

   ---

   Edited 8/31/2005 10:54 pm ET by byhammerandhand

2. 
   jackplane | Sep 01, 2005 04:14pm | #2

   Add naptha.

    

3. 
   Pondfish | Sep 01, 2005 04:51pm | #3

   I'd be leery of using just isopropanol (iPOH) as a solvent, because I'll bet the stuff you get in drugstores will pick up water quickly, or has too much already. But it certainly would be easy to test it out (and cheap)--go ahead and use iPOH for a solvent and compare the result to denatured alcohol (aka ethyl alcohol, ethanol, eTOH, or "alcohol" as in booze).  If it works as well, go for it.  But I suspect someone found long ago it didn't work as well because of the water in it, which is why we all pay more for denatured alcohol.

   Another poster recommended adding naptha.  That might speed up drying, it dries so fast.

   If brushing on the shellac is leaving too many brush marks, why not try padding on the shellac instead of brushing?  Padding works better with faster evaporation, and in my experience it leaves a glass smooth finish. It's fast to do, too, and you won't have to worry about slowing down drying times.

    

   Funny story about denatured alcohol from my school days... eTOH normally will not purify to 100%; it forms an azeotrope with water and the best you can do is get to 95% pure using standard distillation methods.  To make "denatured" alcohol, something else is added to the eTOH while distilling to prevent a water-eTOH azeotrope from forming. 

   When I was a wee undergrad doing histology, a couple of the women in the class thought it would be fun to make peppermint schnaps using denatured alcohol and peppermint sticks.  When someone made a comment in front of the professor about denatured alcohol schnaps, he quickly warned "Don't drink it! You could get leukemia because of trace amounts of benzene used from the denaturing process!!!"

   Never saw someone pale as fast as those two women in the class. 

   That said, I suspect benzene is no longer used in producing denatured alcohol, nor any other solvent with known carcinogenic properties.  So if you're worried about being around denatured alcohol, I would say that using care is prudent, but avoidance may be an over-reaction.  Still, it's a personal choice what kind of nasties you hang around.  

   Recommending the use of "Hide Signatures" option under "My Preferences" since 2005
4. 
   AlanWS | Sep 01, 2005 06:23pm | #4

   My guess is that Minnick didn't want the shellac to dry as slowly as it does with pure isopropyl alcohol as the solvent, and that's why he recommended the mixture. It is possible that you can make a more concentrated solution (higher cut) when you use ethyl alcohol. The film you get should be the same, and if anything, shellac dissolved in pure isopropyl alcohol should have a longer shelf life than that made with ethyl alcohol.

   (For those who wonder about the basis of that statement: Shellac has carboxylic acid and ester groups. Deterioration in solution seems to involve esterification of acid groups, and possibly transesterification of linking esters by the ethanol solvent, to form derivatives that yield a softer film. The more hindered isopropanol should react more slowly.)

   Benzene is not used for denaturing ethyl alcohol. It was once used for making anhydrous alcohol (without the 5% water that remains after purification by distillation) but is not used for that purpose in the US any more. I think that methanol is the usual thing added to denature alcohol. It is toxic, and can cause blindness or even death if you drink enough of it, but it is not likely to cause a problem if you don't drink the dentaured alcohol, and ventilate as you use it.

1. 
   Biscardi | Sep 01, 2005 11:54pm | #5

   Isopropanol is toxic if you ingest or inhale too much.The methanol in the denatured isn't wonderful stuff either. I'd leave the isopropy alone if possible.

   Isobutyl alcohol is added to some of the proprietary solvents (Bekhol) to slow drying. I never found it that big of an improvement when padding. I am not certain if it would effect spraying shellac.

    I never had a problem with denatured evaporating too fast.

   Frank

   Edited 9/1/2005 4:57 pm ET by Biscardi

1. 
   shellacker | Sep 03, 2005 12:04am | #7

   Thanks for responses. As anyone who has tried to sort out benefits vs. drawbacks of the various alcohol types will know, it is an enormously tangled & complicated subject, with a great deal of misunderstanding by end users as a result.

   From what I have been able to determine, Isopropyl Alcohol (I speak only of the 99% pure variety available in many drugstores--NOT standard rubbing alcohol which contains too much water for use in fine finishing) seems to be less hazardous to use than any other type available (except for pure ethyl alcohol which is difficult to obtain and expensive and which by its very nature would contain at least 5% water in any case).

   Denatured alcohol is highly inconsistent. While its main ingredient is ethyl alcohol, it must by law contain poison(s), but there is no specified recipe. The quantity and type of poison(s) is highly variable and usually not listed. It may contain large amounts of highly toxic methyl alcohol (I am aware of samples that contained 16%). It usually contains a small percentage of Methyl Ethyl Ketone, as well as other unappetizing ingredients like Ethyl Acetate. It will frequently also contain some isopropyl alcohol as well, the percentage varying wildly. Of course, the evaporation rate will vary according to the ingredients.

2. 
   Kevin | Sep 02, 2005 02:32am | #6

   My guess is that Minnick didn't want the shellac to dry as slowly as it does with pure isopropyl alcohol as the solvent, and that's why he recommended the mixture.

   I think Alan's right about that. Someone else posted Jeff Jewitt's list of recommended retarders for Shellac which I would trust.

   My experience is more with nitro lacquer rather than Shellac. But, they're similar in many respects. Blending solvents, particularly a hot or "fast" solvent with a cold or "slow" solvent can be a huge advantage for the finisher. Using just a slow solvent can potentially lead to such problems as runs or sags in the finish. Using a blend allows the finisher to avoid some of the problems inherent in using just a fast solvent without running the risks inherent in using just a slow solvent.

   Essentially what a blend does for you is that the hot solvent evaporates quickly out of the finish which allows you to put more on, particularly on a vertical surface, without it running or sagging while the small amount of slow solvent in the mixture evaporates more slowly which keeps the finish material from skinning over too quickly... which is the chief culprit in overspray and orange-peel problems.