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I’m curious as to what was the finishing methods of the old coveted Martins Shellac, Nitro, or some kind of oil varnish? How was it applied?

A really good resource is this massive wall of text website

http://www.earlymartin.com/EM.finishes.html

It's got alot of interesting notes. Basically in the early 30s they went to a lacquer finish. By the mid 30s everything was lacquer just to meet the demands of making more guitars than they had before and it was done to save time and keep the production going.

Before the 20s they mixed some stuff up. Pre-1900 everything was shellac. They probably used a spray gun for the lacquer, cheapest and quickest way to do it consistently. They also buffed the higher end models more because shiny stuff sells better.

I don't know why I had the notion that all the guitar-building Gnomes at Martin back then lived in an enchanted forest and used Pixie dust or Moonbeam paint. Surely not nitrocellulose chemicals!

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My understanding of the history of it is that Nitro was used on cars as a finish starting in the 1920's and the guitar industry started using it shortly there after. So probably around 1925-ish was when you started seeing nitro on guitars.

Wait a minute what’s that on the far right? I knew they made some arch tops but that has no f hole or anything?

From one of the best summaries of changes to Martin design and production specifications:

pre-1900: French polish.
1900: Thin shellac.
1919: Semi-gloss shellac.
1923: High-gloss shellac.
1926 (some models), 1929 (most models): Clear nitrocellulose lacquer. Style 18 models fully switched over to nitro cellulose lacquer by 1929. The transition from shellac to lacquer started in 1926 with O-17H.
1930: All styles have nitrocellulose lacquer finish.

http://www.guitarhq.com/martin.html

We did see some disagreements between the GuitarHQ dates and other sources, but in general, found the site to reflect the consensus of the repair people over on the UMGF and most of what Martin has released from their archived production records.

Greenridge saw a fair number of older Martins from the Golden Era and after, and those instrument finishes seen seemed to confirm the dates above for at least lacquer. Shops specializing in 19th and very early 20th c. Martin instruments might be able to fill in the blanks here, as we saw perhaps a handful of pre-1920 instruments per year. As to the why of Martin's switch to lacquer in the late 1920's? We can blame the need to increase production and commercial availability of the DeVilbiss Company's production lacquer spray guns (driven by the need on Ford's automotive production lines for both speed and precision application of lacquer finishes without tedious handwork to finish the job).

If we consider the Golden Era to be 1930-1939 (exempting the tag end of 1939 as Martin narrowed fretboards and revised construction to reduce warranty claims), gloss lacquer over shellac and dyed solvent-based paste wood filler would cover the finish end of things.

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That would be a Paramount Style "L" made by Martin. They are a peculiar specimen - a bit of a take on the idea of a banjo resonator...

Doc

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So am I understanding properly at some point Martin was grain filling, spraying shellac, and then top coating with nitro?

Watch it, wiseguy. What kind of finish Martin used is cosa nostra.


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Shellac is an excellent sealer to use under lacquer.

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John

Watch it, wiseguy. What kind of finish Martin used is cosa nostra.

You gotta be careful around the Martin family. They might make you a Stauffer you can’t refuse.

Yes...with the exception of some changes to materials (e.g., vinyl sealer instead of shellac sealer/tie-coat) and finish schedule (e.g., new EPA-motivated lacquer formulations), also what Martin does today. Keep in mind that there are a number of knowledgeable people that feel that the move to vinyl sealer was a mistake, pointing to the reluctance of Bolteron to hold onto vinyl sealer & topcoat, and the more recent issues with binding adhesive failures that us repair people have had to deal with as otherwise carefully-made Martin instruments from the 20-teens shed their Bolteron, ivoroid, tortoid, and even wood bindings.

If you can spare the time, the UMGF should provide a wealth of information on Martin finishing materials, practice, and quirks for the 1930's period. As a bonus, you also get to keep company with an assortment of builders, repair people, guitar cranks, and brand fanboys/girls with an overriding common interest in all things Nazareth-centric.

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For the times they are a changin'

- Bob Dylan

Would you feel shellac would be an upgrade over the vinyl sealer? I guess I’m interpreting you as many feel the vinyl sealer was at the root of the failures you mentioned above.

Why would finish have anything to do with binding holding? Did they finish the ledge before putting the binding on?

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Hutch

Get the heck off the couch and go build a guitar!!!!

In a nutshell, solvent load.

Our experience at Greenridge was that something was compromising the binding adhesive such that even easy-to-glue materials such as ivoroid, tortoid, and wood - binding materials we very seldom saw have any issues on Martins - would separate and peel off with adhesive residue that behaved like rubber cement (soft; easily rolled off surface). Lots more in the way of issues with top binding separation from purfling than separation along back binding-only trim (no purflings).

Given that Taylor used a very similar /'nearly identical' adhesive (term used by binding department employee to describe the previously used glue) to Martin without issue for the better part of five years, differences between Taylor's UV cure polyester, very low VOC finishing system and Martin's high VOC lacquer finish process beg the question.

In summary, our suspicion was that the binding adhesive was being compromised during sealing, with at least some of the vinyl sealer VOCs being picked up by the adhesive, then dosed again with VOCs during topcoats. Not something Taylor would have seen with their polyester finishing system, and from what we heard at Martin, something that only longer duration tests were likely to reveal, versus the shorter duration testing done before adopting the problematic adhesive. Also, given Martin' stated reason for adopting that adhesive was to reduce VOC exposure for employee and create a 'greener' environment, adding VOCs to a low-VOC glue line seems like an invitation for downstream issues.

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For the times they are a changin'

- Bob Dylan

Plain and simple, I have never liked vinyl sealer. It seems to be soft and gummy (hard to sand) and has a strange milky, blue look under certain types of lighting.
Most of my guitars have had no sealer, just thinned lacquer for the first couple of coats. On rare occasions, there has been some bleeding of rosewood coloration onto the binding or backstrip, but scraping it off before succeeding coats was all that was required.
I mainly use clear shellac on the soundboard to avoid getting stain or pigmented grain filler on the spruce, which woul be disastrous. I can also use lacquer for the same purpose. Shellac is friendlier, though, and can be brushed.

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John

+1 for skipping sealers and "self sealing" with lacquer - greater clarity and fewer problems.

I'm not sure what vinyl sealers were tried, but at least the Mohawk EZ Vinyl Sealer 550 (the higher VOC version - not the 275) and the McFaddens I used early in my time at Greenridge applied and sanded like plain lacquer, and were invisible under finish. I would agree that sanding sealers - as opposed to vinyl sealers - sand poorly and can reduce transparency, but that is likely due to the silicates added to bulk the film and failure to apply a 50/50 wash/burn-in coat to melt sanding scratches.

As I often got stuck with the scut work of final prep and sealing before color or topcoats, I actually began to enjoy the process of making sure filling, sanding, and toothing artifacts did not translate to a visible issue such as reduction in transparency or haze. One thing we always did between sanded layers of finish - whether sealer, color coat, or top coat - was to make burn-in as efficient as possible by applying a 50/50 lacquer/lacquer thinner coat over any sanded surface.

_________________
For the times they are a changin'

- Bob Dylan