Hardener for shellack


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10 minutes ago, jacobsaunders said:

I have no chemical knowledge at all, I'm afraid, but I would add some sanderac to it

Ive used shellac with around 25% sandarac  for alot of things. The film hardens faster and the shellac stops the cracking etc.. often associated with straight sandarac.

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Shellac is only a solution. It hardens by having the solvent evaporate out of it. That's different from oil varnish, where the varnish reacts with the oxygen in the air, and a siccative (drying agent), like some metal salts will catalyze the reaction. So, there is no additive that will do that with shellac. Warm air blowing over it will help.

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3 hours ago, FiddleDoug said:

Shellac is only a solution. It hardens by having the solvent evaporate out of it. That's different from oil varnish, where the varnish reacts with the oxygen in the air, and a siccative (drying agent), like some metal salts will catalyze the reaction. So, there is no additive that will do that with shellac. Warm air blowing over it will help.

Agreed. Shellac is pretty inert, and mostly hardens from solvent evaporation. But solvent evaporation from shellac can be pretty slow. It is still considered to be a pretty effective "barrier coating" for moisture and grease penetration,  also some solvents. The Zinsser shellac-based paints I have used on the inside of my shower have outlasted other paints by a factor of roughly 5 to 10.

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6 hours ago, David Burgess said:

Agreed. Shellac is pretty inert, and mostly hardens from solvent evaporation. But solvent evaporation from shellac can be pretty slow. It is still considered to be a pretty effective "barrier coating" for moisture and grease penetration,  also some solvents. The Zinsser shellac-based paints I have used on the inside of my shower have outlasted other paints by a factor of roughly 5 to 10.

Do you mean this product? The problem is that I can't buy Zinnser paints in Japan. 

 

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9 hours ago, FiddleDoug said:

Shellac is only a solution. It hardens by having the solvent evaporate out of it. That's different from oil varnish, where the varnish reacts with the oxygen in the air, and a siccative (drying agent), like some metal salts will catalyze the reaction. So, there is no additive that will do that with shellac. Warm air blowing over it will help.

Thats what o figured out too. Is there eventually a solvent which evaporates quicker?

Here in Japan humidity is pretty high all year long and rather than warm air maybe a dehydrated chamber is better.

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10 hours ago, fiddlecollector said:

Ive used shellac with around 25% sandarac  for alot of things. The film hardens faster and the shellac stops the cracking etc.. often associated with straight sandarac.

Will definitely try it. So that's basically 3 parts shellack and 1 part sandarack, right?

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Still waiting for someone to point out that bleached dewaxed shellac has a shelf life. After a couple of years it's both harder to dissolve and won't dry. If you shellac is absolutely colorless, it's bleached. I have had a similar problem with very old batches of regular unbleached types not drying. Talking 10+ years old in my case. This isn't a matter of solvent release. . . iit's never going to harden, ever.

Normally shellac is an incredible covering. It acts a bit like hard leather in that it doesn't chip, but also doesn't wear, and is flexible over moving surfaces. Old shellac oxidzes/polymerizes and becomes totally insoluble, so used alone it's a particularly poor choice for retouching and overvarnishing. Pure shellac with color is a very durable violin coating, doesn't look bad, and has some desirable tonal characteristics. If I were running a violin factory, that might be what I'd use.

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Shelf life seems to depend on how the shellac was originally processed. Years ago, I contacted Zinsser directly (they are the world's largest shellac producer, employing actual chemists etc), and asked what their  most stable form was. Their answer was that it was their de-waxed, charcoal-purified (rather than chemically-processed?) blonde flake product, so I purchased some from them, since it is not a normal "off-the-retail-store-shelf" product. It still seems to dissolve and dry fine, after 30-40 years or so. However, it does seem to have a shelf life once it has been dissolved in alcohol. Apparently, the alcohol reacts with it somehow over time, messing it up.

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1 hour ago, David Burgess said:

Shelf life seems to depend on how the shellac was originally processed. Years ago, I contacted Zinsser directly (they are the world's largest shellac producer, employing actual chemists etc), and asked what their  most stable form was. Their answer was that it was their de-waxed, charcoal-purified (rather than chemically-processed?) blonde flake product, so I purchased some from them, since it is not a normal "off-the-retail-store-shelf" product. It still seems to dissolve and dry fine, after 30-40 years or so. However, it does seem to have a shelf life once it has been dissolved in alcohol. Apparently, the alcohol reacts with it somehow over time, messing it up.

The raw shellac that I bought more than 30 years ago still dissolve perfectly, it seems that chemical treatment for processing is the main responsible for the short shelf life when dry.

On the other hand, once dissolved in alcohol an esterification process takes place (esterification of free carboxyl groups, with formation of semi-liquid, viscous and sticky alkyl esters) which makes it soft and rubbery forever when it is dried and less water resistant. Industrially some chemical additives are used to limit this and prolong the expiration date of ready-made shellac varnishes.

Extensive studies on shellac have been made and published by Claudio Canevari and Silvia Zanchi for the I.R.O.R. (Institute for Organological Research and Restoration - Milan)

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Michael, David and Davide have all shared good and valuable information.  The only thing I would add is that if you wish for it to dry as quickly as possible, mix up fresh batches for each project.  After a few days the drying time starts to increase.  I simply put a fan on things I want to dry quickly.  Heat of course helps, but there are of course risks...

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I will agree with Mark and Davide, in that shellac, once mixed with alcohol, seems to start deteriorating and losing its original properties very quickly.

I was just looking at some of my past experiments, some using "off-the-shelf" shellacs which had already been mixed with alcohol for a year (assumed, based on the expiration date on the can), versus my outcomes with freshly mixed shellac.

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On 8/4/2020 at 6:55 AM, fiddlecollector said:

Ive used shellac with around 25% sandarac  for alot of things. The film hardens faster and the shellac stops the cracking etc.. often associated with straight sandarac.

Would you know what gum thrus is?  The old Petherick book mentions it's use to be used carefully if the shellac/sandarac mixture is turning out to be too hard for violin work.

All I could find about it was a baby's mouth disease.

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18 hours ago, Mike_Danielson said:

https://www.thewoodworks.com.au/shop/consumable/shellac-hardener/hardener-to-formulate-hard-shellac-polish-detail

This is a hardener for shellac. 

You can also put the instrument in the UV box--shellac will harden overnight.

Mike D

Mike, 

this looks very interesting. Thanks a lot.

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On August 6, 2020 at 3:33 AM, Mike_Danielson said:

https://www.thewoodworks.com.au/shop/consumable/shellac-hardener/hardener-to-formulate-hard-shellac-polish-detail

This is a hardener for shellac. 

You can also put the instrument in the UV box--shellac will harden overnight.

Mike D

In the meantime I tried to get the hardener from them but they can't ship flammable goods to Japan, 

too bad 

thanks anyway.

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If I were to use a "hardener" for shellac, I would need to be assured that the hardening would stop at a certain point, prior to it becoming too brittle.

For the most part, when using shellac, I have found softeners to be more valuable than hardeners, over the long haul.

But I will again stress that not all "shellacs" behave the same.

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I haven't had dissolved shellac go bad since I started using anhydrous alcohol (bioethanol sold as fuel for stackless fireplaces). I guess it's the water content in most alcohols that causes deterioration. I have some flakes 20 years old that work well and I still use bottle of dissolved shellac I prepared almost 5 years ago for french polishing. I typically don't wait more than 3 days after final coats before stringing my mandolins.

Interestingly I never considered shellac soft or needeng hardener of any kind... perhaps a bit of plasticizer.

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22 hours ago, David Burgess said:

If I were to use a "hardener" for shellac, I would need to be assured that the hardening would stop at a certain point, prior to it becoming too brittle.

For the most part, when using shellac, I have found softeners to be more valuable than hardeners, over the long haul.

But I will again stress that not all "shellacs" behave the same.

I am experiencing just the opposite. Layers which should be hard enough after one week are too soft taking imprints from whatever surface they are touching. Could be humidity related as well.

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