So you want to formulate your own varnishes.

[Jelly]

Following on from MIGNAL's post.

I wasn't aware that Shellac would go into an oil based varnish.
How are you making the Shellac, rosin and linseed oil varnish? Are you heating this until you reach the long string stage? You will also need to add a drier and/or subject it to lots of UV to get it to dry and harden in a reasonable time.
Any resin/oil varnish should be able to produce a pretty glossy surface if you go through the grits/polishes, providing the oil to resin ration isn't too high. In any case these sorts of varnishes aren't what one call hard wearing. You really have to go to the short amber/copal varnishes or the harder synthetic resin varnishes to get hard wearing. Behlens used to do a synthetic oil varnish that was really hard and tough. Dried fast too. I suspect that a lot of the stuff sold as 'table top' or 'bar top' varnishes will be very similar too.

This will get increasingly chemical, so I apologise if it bamboozles anyone just ask and I'll try to make a more detailed less technical explanation.

Shelac is composed of long chain organic acids, they're almost insoluble in "Non-Polar Solvents" i.e. Mineral Spirits, Natural Turpentine etc.

But, subject to pH effects they're very soluble in "Polar Protic Solvents" i.e. Ethanol (Grain Alcohol) and Methanol (Wood Alcohol), which are infinately miscable with non-polar solvents.

Linseed Oil and Rosin are miscable with both Polar and Non-Polar Solvents, (It's possible, but not easy to solvate the Rosin in hot linseed directly, much easier to use a Non-Polar solvent to help it along).

The trick is to find a solvent, or solvent blend which will happily solvate both the Shelac and Rosin, and remain miscable with the linseed oil, a "Mutual Solvent".

I've experimented with various mixes, and it's not always worked smoothly either, as you can unwittingly drop the shellac solids out as a precipitate if you don't have enough of the mutual solvent in the mix, but too much solvent will leave insufficient linseed relative to the solids to polymerise into a matrix which bonds to the surface, rather than just dry onto the surface as a deposited coating.


Interestingly, the components of linseed oil and shellac are structurally quite simmilar and both undergo some degree of cross linking with exposure to oxidative processes, via different chemical reactions.

Rosin is the odd one out structurally, with a rather different structure which is not as conducive to cross linking in its natural form; however when esterified with by acid catylised reaction with an alcohol it develops that property, as 'ester gum' which is important in commercially available varnishes, (when reacted with a polyol, it would be a form of Alkyd), this polymerisation is chemically simmilar to the one which shellac can undergo.


With regards to drying, there are a couple of ways to achieve the same effect, UV will increase the frequency of the Free-radical reactions which integrate oxygen (as hydroperoxy groups) into the unsaturated tails of the fatty acids making up the oil, a catalyst (moden drying agents) will reduce the energy needed for that to happen increasing frequency, and finally introducing more oxygen will increase the frequency by providing the reactant where it's needed (this is what older drying agents, like lead dioxide or chromium trioxide did).

 

[MIGNAL]

You need to go on the violin forum, maestronet. They'll happily talk varnish and varnish making until the end of time. It's nearly always natural resins in linseed or walnut oil. Shellac does crop up from time to time. There's even a commercial varnish maker on there but many have a lot of experience of making home cooked varnishes. I did a few pine resin/linseed varnishes myself but found it too time consuming. The fumes can be a bit nasty and I'm not fond of exothermic reactions either. A lot of them do a very long slow cook (days) to get decent colour into the varnish.
Don't mention Alkyds or Nitro You might have to put up with a bit of wood treatment too. They'll be interested in chemmy types.

 

[bugbear]

The fumes can be a bit nasty and I'm not fond of exothermic reactions either.

To be explicit, that's "exothermic reactions in liquids that are both flammable and volatile"

Yummy. :shock:

BugBear

 

[Jelly]

The fumes can be a bit nasty and I'm not fond of exothermic reactions either.

To be explicit, that's "exothermic reactions in liquids that are both flammable and volatile"

Yummy. :shock:

BugBear

Going back 4 years my "daily grind" was carrying out untested reactions which were predicted to be highly exothermic on upto 5kg of highly toxic solution , with pyrophoric liquids and high-pressure flammable gasses. We used to keep liquid nitrogen baths in the fume hoods, so if something ran away you could freeze it and inject a quench solution to deal with the problem when rewarming it.

I discovered my all time favourite line in a scientific paper during that time; "warmen de kolf een beetje, maar niet te veel"
Which I understand is Dutch for: "Heat the flask a bit, not too much!"

That kinda stuff never gets (entirely) boring, but its actually pretty safe really!

 

[DennisCA]

Here's a formulation I intend to try this summer to use on outdoor furniture:
15% varnish (basically epifanes)
15% pine tar (the good kind)
20% turpentine
50% oil (tung & linseed)

It's based on a commercial product I tried to retro-engineer.

 

[MIGNAL]

The very first batch that I made the oil caught fire. I also allowed the pine resin to get far too hot, effectively burnt it. Still, I carried on and mixed the two together. It was still a varnish, it just had a yucky green tinge to it. It dried very fast considering it was an oil varnish that did not have an added drier. I assume that was because of the high heat.
Somewhere I saw an illustration of a varnish maker from the 17 th or 18 th century. The actual cooking vessel was on rail track, presumably so they could get it out of the way just in case the thing caught fire! There have been deaths and some very nasty injuries associated with this kind of varnish making. You really do need the correct equipment and safety procedures.
My second batch of pine resin varnish was much more successful. Smells divine. Far better smell than modern synthetic varnishes. I still make spirit varnishes. Much easier (and safer) to make than oil varnishes. They can smell divine too, especially if you put in a bit of gum benzoin and a few drops of spike oil of lavender in.
Somewhere I have a batch of amber oil resin that my friend made many years ago. It's supposedly very difficult to make because the amber has to be heated to a very high temperature. There's probably a bit more to it than that because many people seem to fail at making it.
Fascinating subject.