Several weeks ago there was a post, which I can’t find now, about the best alcohol to use to dissolve shellac. The consensus seemed to be that denatured ethanol gave a reasonable drying time and was readily available.
Here in Canada, it’s almost impossible to find denatured ethanol. What we use for shellac is methanol — or as it’s called here, methyl hydrate. It’s true, it dries really fast, so you have to be quick. But that means you can put maybe three coats on in an evening.
I think that shellac will dissolve easily in any alcohol — methyl, ethyl, isopropyl, and so on. The only real difference is the drying time — short, for methyl, longer for denatured ethyl, and if you wanted to add isopropyl (rubbing alcohol), that would increase the drying time even more. Just make sure your rubbing alcohol doesn’t contain water.
Replies
"Just make sure your rubbing alcohol doesn't contain water."
Grant,
As I understand it, that's precisely the problem with isopropyl alcohol - it's hygroscopic.
-Jazzdogg-
"Don't ask yourself what the world needs. Ask yourself what makes you come alive, and go do that, because what the world needs is people who have come alive." Gil Bailie
>> As I understand it, that's precisely the problem with isopropyl alcohol - it's hygroscopic
All alcohol is hydroscopic as far as I know. Iso may be more so, but the primary problem is that iso alcohol is frequently used for rubbing alcohol or sterilization and is not made to be totally water free in the first place.Howie.........
As far as I know you are right about all alcohols being at least partially hydroscopic. I've got a very handy solvent guide that lists about a dozen alcohols and all of them are hydroscopic to varying degrees.
Noteworthy for this discussion, both Isopropyl and Methyl alcohols are 100% hydroscopic and it works both ways... ie., both alcohols will mix fully if poured in water... and water will mix fully if poured into either alcohol. Ethanol is the other main alcohol that this list says is 100% hydroscopic. All of the others are only partially so, with some being barely hydroscopic.
Part of the problem inherent in working with these fully hydroscopic alcohols is that even if you buy it pure (without any water in it), they will pull moisture from the atmosphere. Which is why lacquer's will blush under certain conditions.
Kevin,
A few small points.
All alcohols are hydroscopic. Hydroscopic refers to their affinity for atmospheric water. Left open to air, they will absorb water from the air at a rate depending on 2 variables: the amount of water in the air and on their various hydroscopic affinities.
Another measure of a chemical is the ability to mix with a given quantity of another. All alcohols can mix with water, in any proportion. That is, alcohol and water will form a perfect solution, using any ratio of one to the other. They are mutually soluble, they completely disolve in each other.
Being able to mix in any proportion, alcohol and water are miscible. Some people use the expression 100% miscible, as in, "alcohol and water are 100% miscible," but that's redundant.
Any alcohol, left exposed to atmospheric moisture will absorb water, eventually acquiring an absolute absorbed quantity, (assuming no change in the realtive humidity) reaching an equilibrium with the atmosphere, and will be diluted by the amount it absorbs. (And in the case of use for disloving shellac to be used as a wood finish, seriously impaired). But there is no such thing as 100% absorption or a 100% hydroscopic characteristic.
Rich
Yes, I knew that miscible was the correct term. But, I didn't want to go too far off on a technical tangent. So, I stuck with hydroscopic.
As for your contention that all alcohols are miscible with water in any percentage, I'm going to defer to my literature which says otherwise.
According to my ChemCentral solvent booklet, not all alcohols are fully miscible with water. One section of it lists solubility parameters with water. According to it, only methyl, ethyl and propyl alcohols are fully miscible with water.
I've also got an organic chemistry book from 1944 (Elementary Organic Chemistry of Commercial Solvents Products - Charles Bogin) that says the exact same thing - that only methyl, ethyl and propyl alcohols are fully miscible with water in any proportion. As an example... butyl alcohol dissolves only about 8.9 percent water at ordinary tempuratures. Any excess water added to butyl alcohol will not go into solution. The miscibility with water goes down from there until one reaches the octyl alcohols, that contain 8 carbon atoms, which are almost completely none-miscible with water. What's interesting is that miscibility with Naptha is the exact reverse... with the octyl alcohols being very highly miscible with Naptha while the ethyl, methyl and propyl alcohols are almost completely none-miscible with Naptha.
Kevin,
Thanks for that additional information. I stand corrected. Not all alcohols are miscible. Also some wines I've sampled are miserable, but that's another tale.
Rich
LOL - I have had the same experience with some wines... particularly reds, which I have never cared for. I guess maybe I just don't have a refined enough palate. My girlfriend is partial to flavored wines... which pretty much marks us as heretics anyway. ;-)
Anyway... I'm certainly no organic chemist, having never taken a chemistry class in my life. Which is why I have to refer to books and hope that I've understood what I've read. And sometimes I do... I think. Wines are so much easier because they are mostly just subjective and everyone gets to decide what is correct and what isn't. Well... except for us heretics, that is.
In spite of the fact that you may think that "hydro" as a suffix for "scopic" would have to do with "water", it is "hygroscopic".Gretchen
Gretchen,You certainly are correct. And I am chagrined to admit that I have been using the incorrect word for quite a few years! I've no idea when my brain stopped recognizing the correct term, as I remember quite well being aware of it long ago!Embarrassing!"Hydroscopic" apparently refers to a device for listening under water. I have actually been involved in the use of a "hydroscope," but I have never heard the use of the word, "hydroscopic" in that regard.Memory is a terrible thing.Rich
Dang I thought All of it was it's hygroscopic??
Correct. That's why you are not allowed to drink it.Philip Marcou
Grant,
I've worked with Methanol in another industry. It is a great alcohol, but it is a carcinogenic. I'm surprized that you can get that without it being a controlled substance as I believe it is in the US. Just be sure to wear good quality gloves when handling it. It's not something that will hurt you right away. It builds in your system over time. Just be careful....I know we are overly safety conscience in the US, but better safe than sorry.
Woodworker79 ,
Thanks for your message. It's an interesting question: why is (denatured) ethanol available in the US, while methanol is forbidden, whereas in Canada, methanol is everywhere, but denatured ethanol is hard to find. It is available at Lee Valley. They call it Shellac-Lacquer Thinner, and it's ethyl alcohol denatured by isobutyl alcohol. I use it for shellac, especially the later coats. It has a fairly long drying time.
Grant
I've read at least 3 MSDS on Methanol. Not one states that methanol is a Carcinogen. As a matter of fact it has the same health hazards as Isopropyl only stronger. If you have a report or source that states it is recognized as a suspected or known carcinogen i would like to see it. Furniture...the Art of a FurnitureMaker
That information was the word from fellow co-workers. It was enough for me to be careful with it. But I have looked up the MSDS and your right, it doesn't specifically mention it being a Carcinogen. It does list some exposure concerns, so I would still take precautions with using it.Here is the MSDS: http://www.bu.edu/es/labsafety/ESMSDSs/MSMethanol.html
I actually started to respond once before, but deleted it because I figured people didn't want to hear it. (I have that experience, since I am an organic chemist, and I think it's a fascinating subject.)Methanol is toxic to a significant degree because the same processes that can detoxify ethanol work in this case to convert methanol slowly to formaldehyde, and that's quickly converted to formic acid, which itself is made harmless by conversion to carbon dioxide. The most prominent effect of methanol poisoning is blindness, caused by accumulation of the formic acid faster than it can be destroyed, but enough methanol will certainly kill you. Because of person to person differences, people have survived doses that are 30 times higher than those that have killed others. I haven't looked up the numbers, but I think isopropyl alcohol is substantially less toxic than methanol.The questions of carcinogenicity arise because formaldehyde can be carcinogenic, but that's also subtle. Much more carcinogenic than formaldehyde are substances formed by exposure of formaldehyde to other chemicals like HCl. Formaldehyde by itself appears to be carcinogenic as well, but I think that's been demonstrated only if you breathe it. So there is a big question how much formaldehyde you would be exposed to after contact with methanol, and other questions about what the effect would be, given its location in the body, and that the body can detoxify it. If you get a big dose of methanol, you have problems much more urgent than cancer. If you have low dose exposure over a very long period of time, it's possible that you might have a measureable cancer risk. I don't think it's been measured though, and would expect that to be difficult.Incidentally, one treatment for methanol poisoning is to give ethanol. (I don't know whether it's a current treatment, but it's been used in the past.) This apparently keeps the enzyme busy that could convert methanol to formaldehyde. I suppose it also keeps you from worrying about anything during treatment. If you want reliable information on things like this, when you go to google, click on the "scholar" button and do the search there (for something like "methanol" and "toxicity"). That will find hits with the proper citations to allow evaluation of reliability.
Alan, I would not disagree with what you have stated, except for the fact I don't think anyone using Methyl alcohol for Shellac is going to consume it. I would like to think the only interaction would be thru skin contact and or inhalation. How many know Methanol is what Indy cars run on?Furniture...the Art of a FurnitureMaker
I was actually trying to point out it's not so bad, even though there is a possibility of carcinogenicity. In any case, it's less toxic and carcinogenic than gasoline.
Edited 9/25/2005 10:52 pm ET by AlanWS
Here in Italy you have to be liscenced to buy methanol. In 1985 they grape crop was low in sugar so the wine fermented to a low alcohol percentage. Some disreputable wine makers added methanol to their wine to boost the alcohol up to the legal minimum of 12%. (really cheap wines not the real stuff)
Killed a number of people, blinded alot of others and caused minor problems for scores of others.
After this methanol is carefully controlled..... so are wine producers.
Philip
I worked as an engineer on a production process that needed a solvent. I'm a mechanical, not a chemical, engineer so I paid close attention to MSDS data. I do not recall any of the alcohols being carcinogenic, but I do remember that methanol was considerably more toxic than isopropanol. Methanol is easily absorbed through the skin. Isopropanol is, of course, used as rubbing alcohol so is not harmful to apply to the skin. Only certain types of rubber gloves provided protection for methanol, others passed methanol right through them.
We required our employees to work with methanol under a fume hood because of the low level of exposure that was needed to be safe.
It's been a few years since I looked a the literature, but I would not use methanol for anything in my home shop.
I noticed the same thing, you read all the posts and the americans can buy denatured alcohol everywhere but ib Canada hard to find.
Found sonme here though:
http://www.finition-de-meubles.com/bienvenue.htm
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