Your favorite oil varnish

[Truckjohn]

Hey all

What's your long oil varnish of choice and what schedule do you use for thinning and finishing?

I am brushing, not spraying or wiping.

Behlen's Rock Hard has gone urethane..... I have not had good luck with urethanes.... And my last can of "The Good Stuff" has turned to a solid lump....

What's out there? I have seen Tru-Oil, Epifanes varnish and their Epifanes wood finish... Sherwin Williams and Ace varnish. Al Carruth posted about some Murdoch's "Ure-alkyd 500" product.... Pratt & Lambert #38....

Thanks

[capohk]

...here:

http://www.acousticguitarforum.com/f...d.php?t=441996

[Alan Carruth]

I don't believe that Behlen's old 'Rock Hard Varnish' was a 'long oil' varnish; it seemed more like a 'short oil' or 'rubbing' varnish. Oil-resin varnishes are made by cooking a drying oil with a resin to form a co-polymer. Depending on a lot of factors you can come up with very different properties in the final film. One big variable is the proportion of resin to oil. The film properties will usually broadly mirror the proportions. 'Long oil' varnishes, with as much as parts oil to one part of resin, tend to act like oil finishes to some degree. They still form a good water resistant film, but it's flexible, and often will get soft with heat or high humidity. These are often called 'spar' varnishes, because they are flexible enough to weather well without checking. 'Short oil' varnishes can have twice as much resin as oil, and tend to form a harder and chipper film that is more stable in the face of heat and humidity, but can check with large changes in either. They usually polish up well, which is why they're called 'rubbing' varnishes.

These days I'm using Murdoch's Ure-Alkyd 500 floor varnish. In many ways it's even better than the old rock-hard. The one big issue I've had is getting it to cure properly on some oily woods. It would not be as bad if you could predict when that was going to be an issue, but so far I've had problems with some pieces of most of the tropical woods I've used. In some cases even stopping the wood out with a coating of shellac doesn't totally cure the problem. It's too bad; otherwise this is a great finish.

[Truckjohn]

Al,

You are right about the long vs short oil varnish. I am after a good "short oil" varnish rather than a spar varnish.

I checked out the Murdoch's product.. Looks like it's only available online for me.. And it's also a urethane product rather than a phenolic resin sort of thing. If I could get some locally - I would be all over it.... And I still might give it a crack.

What is your thinning/mixture schedule with it? Is it fairly forgiving of thinner selections or do you have to use their Di-citrusol stuff?

Have you tried the new Rock Hard urethane base varnish? If it behaves like the old one - it may be still be a winner.

As an aside - I have some home made pine tar from another project. Makes me wonder about cooking up a "varnish" made of pine tar and some sort of drying oil. Might be interesting. Alas - I don't need yet another hobby.

Thanks

[Alan Carruth]

I use the Murdoch's right out of the can.

The problem I've always had with urethanes is that they're fussy about re-coat time. You have to let them sit long enough to level sand between coats, but if you leave them too long the next coat won't adhere properly. Often they say 'recoat in six hours' or some such, and I just can't pull all-nighters in the shop. I've had them peel like a bad sunburn. This stuff seems to harden from the bottom up, and I've never had trouble with the next coat adhering properly. Knock wood...

Many moons ago I made up a batch of 'Fulton Varnish'. It was an adventure. You start with a gallon of 'pure spirits of gum turpentine' (accept no substitutes!). Add a few drops of ferric acetate and a few drops of Courtrai dryer (cobalt napthenate), heat it to about 140F with an aquarium heater, and aerate for a month or so with a bubbler. Note that his stuff WILL eat up clear PVC aquarium tubing. You cook off about half of it (nasty fumes), and the other half polymerizes to a honey like consistency.

Set up an electric hot plate outdoors. Put a couple of inches of the thick terpene into a deep sided pan, and have another nearby with water in it. Heat the stuff slowly. At about 125C the hydroperoxides formed during polymerization will kick over, forming water and oxygen, and releasing heat. As the stuff heats up the reaction goes faster. The water comes out as steam, so it foams up more or less instantly: that's why you use an electric hot plate and a deep pan. As soon as it starts you move the pan from the hot plate to the pan with the water in it to keep it from getting any hotter until the reaction stops. The ferric acetate helps cut this down, and gives the finished varnish a red color. Once the stuff stops foaming, you can finish cooking it.

The hotter you get it the darker the resin will be. When you judge it to be the right color you can add raw, cold pressed oil. Linseed will dry faster, but the Italians used walnut oil. Don't use olive oil; the varnish won't dry, but will turn rancid. You may need to cool it down a bit first. It gets cooked at a certain temperature (I'm not looking at the recipe at the moment, so I can't say what that is) until it forms the co-polymer. you test for this by putting a drop of the goo on a glass plate and seeing if you can draw out a 3' long thread from it. At that point you add in some regular thin turpentine, and you've got varnish. And the whole neighborhood is smoky...

This stuff requires strong UV light to harden.

In his book on artists materials Ralph Meyer says that it's impossible to make oil-resin varnish in batches of less than 200 gallons and achieve decent quality control. The properties of the final product depend not only on the oil and resin used, and the proportions, but also on how high the temperature goes, how long it's held at that point, how long it took to get there, and how fast it gets cooled off. You could quibble with his 200 gallon number, but it's pretty plain that cooking the stuff in the back yard is not likely to produce predictable results.

The batch of Fulton varnish I made looked great, once I got it to dry. If you read a book like Hill's, they frequently comment on the variability of the varnish; sometimes it's really nice and sometimes it's far from that.

I've still got a jar of the thick terpene: I can't get the lid off it. Maybe some time I'll cook some more varnish. It depends on how desperate I got for excitement..

[Truckjohn]

Hmmm... Make my own varnish you say... I mean I am a chemical engineer and all...

No wonder you are my wife's favorite luthier . She wouldn't even be surprised that I was making my own varnish.....

I can imagine the conversation now...
What's that smell and all that smoke?
Oh - I am making my own varnish.
Inside the house?
Well - it's too cold outside and it might rain in it, and it would explode...
Humph!
Well, I do have a fire extinguisher handy......
Will it come off the cabinets?
Probably not once it's cured....
Where did you find out about this?
There's this luthier Al Carruth online who explained the whole process...
That name sounds familiar... Is he the one that got you going with the black pepper and loud speakers?
Yes, that's the one! Wasn't that cool!