Maybe stupid question

Re: Maybe stupid question

HC Sakman

>Hi Matti,

Lacquer is basically synthetic shellac, which is a secretion of the lac insect Coccus lacca, found in the forests of Assam and Thailand. Freed from wood it is called "seedlac."

It is soluble in alkaline solutions such as ammonia, sodium borate, sodium carbonate, and sodium hydroxide, and also in various organic solvents.

When dissolved in acetone or alcohol, shellac yields a gloss and hard finish. Orange shellac is bleached with sodium hypochlorite solution to form white shellac.

Most natural varnishes consist of a gum or resin dissolved in a solvent. Depending on the solvent used, the three main types of natural varnish are spirit varnish (which uses alcohol as a solvent), turpentine varnish, and oil varnish. Spar varnish (also called marine varnish) is high quality waterproof and sunlight resistant varnish named for its use on the masts of ships (called spars). Nowdays polyurethane/urathane (I don't know the exact difference in between them, both work and behave the same way) is made as synthetic varnish. It does not contain natural rasins.

Turpentine is a solvent obtained by distillation from tree resin, mainly various species of pine (Pinus). Alternative names are wood turpentine, spirit of turpentine, oil of turpentine and gum turpentine. It is also known as just "turps", although this more often refers to turpentine substitute (or mineral turpentine).

Paint thinner is made of petroleum distillates, like karosene, naphtha and varsol.

I don't know how lacquer thinner, Xylene and acetone are made, but I suspect petroleum products play a major role.

Briefly:

Lacquer's solvent is lacquer thinner, xylene and acetone. Lacquer can be coated with varnish but varnish can not be covered with lacquer.(Solvents in the lacquer will dissolve varnish.)

It can be mixed with retarder solvent and used as "brushing lacquer". Lacquer can be effected by high moisture, heat(like hot cup of coffee) and alcohol. Newer nitro-lacquers are made tougher. Lacquer is usually sprayed and it can easily be colored. It dries to touch in seconds, can be used in 6 hours but it really cures (reaches its full hardness) in a week. Otherwise it's clear.

Varnish's solvent is paint thinner, turpentine and naphtha.(as well as mineral spirits, varsol etc...) Varnish is tougher than lacquer. Actually "durable" is a better word. It's less scratch resistant than lacquer. Varnish has an amber color. It dries slow, in 4 to 12 hrs. It can be used after 24 hrs of the last coat and fully cures in couple of weeks.

Shellac's solvent is alcohol. Don't use vodka though! ;-) That would be a waste! Methyl alcohol is commonly used to dissolve shellac flakes and for clean-up. It's a nice quick finish. It's not tough though. It can be easily scratched, not much moisture resistance and obviously can not stand alcohol and heat. Dewaxed version can go under pretty much any other finish, therefore it can be used as a sanding sealer. It comes in clear (called white shellac) and different shades of amber (called orange, buttonlac, seedlac...) and can be used for its color effect.

I have no idea about the details of water based varnishes.

That's pretty much it.

Chico...

BTW, I forgot OILS...

HC Sakman

>Oil is oil, really. "Oil finishes" though contain metallic dryers and/or some varnish to form a film finish. (Danish oil finish is one. Wiping varnish(poly) has more resins in it than Danish oil.) Most furniture oils are made from sunflowers and flaxseed(linseed). Other ones are names as thier sources. Walnut, tung, teak etc...

Chico...

Now I know, thanks

Matti Kuikka

>

more on finish and how different

bill tindall

>Lacquer is a general term for a finish that consists of a solution of a film forming polymer in a solvent. Apply the lacquer and the solvent evaporates leaving behind the polymer film. In modern lacquers there can be additives that cross link the polymer after application. Traditionally lacquer is made by nitrating cellulose (just like gun powder, but with a different amount of nitration). Modern lacquers may contains other film forming polymers which can be other derivitives of cellulose or acrylic polymers. The solvent will be a mixture of chemicals formulated to control drying time. One wants the lacquer solvent to begin drying quickly so it will not run but then stay wet long enough to flow out and level the finish. This is why a properly formulated lacquer is easy to apply and get a good finish.

Varnish is very different from lacquer. Varnish consists of some chemicals that react after application to form the polymer film. Traditional varnish is made from natural product oils dissolved in a solvent. These oils have places in their molecules that react with air and this reaction joins these molecules together to make a crosslinked polymer. The formulation may contain additional chemicals, for example isocynates(urethane varnishes) to cross link the ingredients. Once exposed to air the curing reaction begins. This is why a partial can of varnish will set up even when it stays sealed so the solvent can't evaporate.

Summary:

lacquer- film forming polymer already in the can. Finish will redissolve. Stable indefinitly.

Varnish- film forming polymer formed after application, usually by reaction with air. Finish may soften but it will not dissolve after curing. Material can react in can , so product has a shelf life.