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I have a very different takeaway from Martin Schleske's publications. In his 1998 article for the Catgut Journal, and currently on his website, he shows that some finishes reduce the damping of the wood they're applied to, while others cause a large increase in damping even if applied thinly. The composition of pore filling materials and sealer coats may have an even more profound effect. These effects change over time, and may take a decade or longer to settle down. All of this fits with my own experience.

You can view the 1998 article here: https://stacks.stanford.edu/file/druid: ... kq5616.pdf (The article begins on page 29 of the PDF.)

Very dense and interesting article, I’m only part way through, but…what fin ish have you settled on?

Durability and tone are two factors. How about repairability? I rate this as an important factor also. In my repair business I’m constantly managing customer expectations on modern urethane and polyester finishes, in terms of what some ding or scratch will look like after drop fill or touch up. Most are disappointed to discover that CA fills on modern finishes can look good but are often not completely invisible from every angle.

Those with nitro (or shellac) finished guitars enjoy much better looking repairs.

Even the most durable modern finish can end up dinged, cracked, chipped, lose adhesion to its substrate. What then?

My wife scraped the side of her car last month. Total respray of the affected panels is required to achieve a seamless repair, according to every panel shop in town. I think going in this direction with guitar finishes as well is not the value proposition for customers that it might at first seem. Don’t take my word for it, ask a local repair shop how much they charge for a strip and refin of a tough modern finish.

Just my perspective as someone who spends his days looking at the scratched, the chipped, the dinged masses yearning be shiny.

I French polish with shellac over a shellac/pumice pore fill. I only build classical and flamenco guitars, so there's more acceptance of shellac's vulnerablilities, but we also do French polish finishing for a couple of steel string builders who have persuaded their customers that French polish sounds better. I think the pumice pore fill is a big part of that. You can hear the tap tone brighten within a day after applying pumice. I also like shellac's track record. I'm pretty comfortable dealing with the ways it can be damaged. I don't lose sleep wondering what new problem may suddenly show up in guitars I finished ten years ago.

Thank you for that information. I’m trying real hard not to have to French Polish, but, it seems like I’ll simply need to…

Many of the early guitars built by violin makers had varnished back and sides and bare wood tops (with possibly a thin coating of egg glair). I think they recognized the sound deadening properties of most thick finishes.
Using a thicker film finish on the back/sides and neck, and French polishing the soundboard may be the best compromise where both durability and sound quality are desired. Shellac may not hold up as well to physical abrasion as a thicker finish but it is easily renewed and widely available.

I've seen some much more recent postings by Schleske. The reduction in damping on a completed instrument with finishes like nitro and shellac is probably 'small' overall, and hard to tease out from other things, so the 'best' finish probably doesn't do all that much to improve the sound. It is, however, easy to hurt the sound with a poor choice of finish, or poor application, or too much, even with the 'best' finish. So finish seems to be a necessary evil: you need it to protect the wood from oils, moisture, and dirt, but beyond the minimum necessary it's a cost.

I just found out that http://www.joha.eu have a special guitar spirit varnish that is harder than the one I've been using for 10 years. When asked what's the difference between the guitar and the standard spirit varnish was, they answered:

"The dry time is pretty much the same. The guitar varnish is harder than the spirit varnish standard,
because in the spirit varnish standard are different soft resins. How big the difference is to the guitar varnish,
I can not say in numbers. But here we use the hardest natural resin, which is spirit soluble."

I also noticed that they now sell spirit varnish as a powder to be dissolved in pure alcohol. That should keep the shipping cost down.

I have ordered a couple of cans of this new harder guitar spirit varnish, the harder, the better!

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turn to ashes or gold

http://www.gammelgura.se

Roger, I have just recently received a response from Hammerl about their powdered varnishes. For a guitar finish to be applied with traditional French polishing technique they recommended the Primer. The difference between the 3 powdered varnishes is the degree of hardness. It would appear violin varnishes increase flexibility and suppleness as the layers get built up. Selling these products in powder form is a stroke of genius. No hazardous shipping surcharges and you could keep the varnish fresher by just mixing up as much as needed.
If there's anyone in the US who wants to split an order please reach out to me. DHL shipping would be much more reasonable for a larger amount of resin/powder. If I remember correctly 3.5 kg was the lowest weight category and was right at $60. So 400g would cost the same to ship as 3.5kg.

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https://www.violincellomaker.com/en-us/ ... h-recipe-1
If the varnish is being shipped as a powder it is most likely a spirit varnish.
Above is a spirit varnish recipe for violins. Spirit varnishes for violins are predominantly shellac with resins and colorants added to increase flexibility and add color (curcuma is turmeric to add a yellow color).
The "harder" guitar varnish is probably pure shellac without the resins added, but I could be wrong.

It's definitely an alcohol based spirit varnish. It just does not make economic sense to ship alcohol overseas when it is readily available locally. Clay, the varnish you linked has many soft resins which would rule it out, at least for me, as a guitar finish. Roger's experience with Joha spirit varnish points to a possible (?) improvement of straight shellac.

_________________
Stay with the happy people.
--Reynolds Large

Hi Tom,
I should have reread the whole thread - I missed the part where Roger said the spirit varnish was harder than regular shellac. Sometimes sellers may name a product for it's intended use rather than it's more common and better known name. Then again, they may have added something that makes it a different product.

I have mixed in other resins with shellac for a ground coat. If you aren't adding color, it is really all that you need. It seems to make the finish just about bulletproof. Maybe I should write down what I did, so I remember? I make it alcohol base first, and then turpentine based. Yeah. It isn't normal; but I wanted it to be good with my oil varnish, that can also be thinned with alcohol. I don't know why.

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Why be normal?