Finish
Loar-signed L-5s had a spirit varnish finish but according to Joe Spann, Gibson began using sprayed nitrocellulose lacquer finish in the second quarter of the year 1925. There does not appear to be an overlap between the use of varnish finishes and switch to sprayed nitrocellulose.
Through to about 1931, the sunburst finish seen on an L-5 was achieved by adding stain to the lacquer, not directly to the bare wood. First the wood was sprayed with a clear sealer coat and then sprayed with lacquer that contained a light coloured stain. Darker lacquer was then sprayed around the edges to create the sunburst effect.

Prior to 1931, the sunburst was produced by applying stain directly to the bare wood and then putting a clear coat over that.

The two methods resulted in an appearance that was quite different. While the earlier process allowed the woodgrain to remain visible over the entire back, the post 1931 finish obscured the grain in the darker areas.
Gibson Cremona Brown Sunburst

The information below originally appeared on the website Mandolin Café and was written by Gibson expert, Joe Spann.
“Like so many of Gibson’s now world-famous innovations, the ‘Cremona Brown’ sunburst finish used on the Master-Model instruments from 1922 forwards was the invention of an obscure employee. Turns out that Master Lloyd Loar had nothing to do with it.
“Here’s a short article from the January 1921 issue of Gibson’s ‘Sounding Board Salesman’ magazine, which identifies the man.

“Not so very long-ago Fred Miller, Foreman of the Gibson Finishing Department, brought into the sales manager’s office, a Gibson mandolin that looked not a cent less than a million dollars. Fred had been taking liberties with the catalog finish specifications and while the F-4 was an F-4 in every other respect, the finish was about “F-100%”, according to our estimation. Practically every girl in the office said she adored it and even the janitor raved over it. In fact, everybody was so enthusiastic about Fred’s work that we forthwith commissioned him to put through a special lot of Gibsons in this new finish, which he calls Cremona Brown. Very soon we expect to have available a few F-4 mandolins, H-4 mandolas and K-4 mando-cellos in this new Cremona Brown finish, which for the time being we will bill at $5.00 additional to the regular wholesale price. If you don’t think the finish is about as beautiful an effect as you have ever seen on a mandolin or violin, just ship back the instrument and we will send it to somebody who likes it.”
Joe Spann adds: “According to my serial number list, the earliest Gibson instrument yet seen with a true ‘Cremona Brown’ sunburst finish is H-4 #65241. According to my revised serial number chronology this instrument would have shipped in August 1921.
“Frederick Martin Miller, the creator of the “Cremona Brown” sunburst was born in Mecklenburg, Germany on 25 February 1885, emigrated to the United States in 1891 and was working at Gibson by 1909. By 1920 he was the Foreman of the Finishing Department and evidently left Gibson at or about the same time as Master Lloyd Loar, Sales Manager Lewis A. Williams and General Manager Harry Ferris, late in 1924.
“By 1926 Fred was working around Kalamazoo as a housepainter, and in 1930 had started his own auto-body repair shop with his eldest son. The Great Depression killed his business, and he was forced to seek employment as a painter at the Checker Cab Company factory. He died in Kalamazoo on 11 February 1944 at the very young age of 58 and is buried there. Ironically, a lifetime of breathing in varnish and lacquer fumes is what likely led to his early death.”

Frederick Martin Miller, above, created the Cremona Brown finish. The combination of ‘burst pattern and wood grain makes every L-5 as unique as a fingerprint!
The L-5s pictured below span a period of approximately ten years. It’s interesting to see how the burst pattern developed over that time.

These examples of finish are from the following serial number guitars
Top row, left to right: 76707, 77405, 81707, 84677
Second row: 85437, 85558, 85758, 86842
Third row: 88290, 88786, 89354, 90303
Fourth row: 90315, 91100, 91522, 91930
Natural Finish
A total of 21 L-5s were shipped with a Natural finish in 1937 and 1938, despite the fact that this option was not officially available until 1939 (this number includes one of the last 16-inch models, which was delivered with a Natural finish in May 1938). The spruce and maple used for instruments with the new Natural finish had to free of flaws that might have been concealed beneath the darker areas of a Sunburst finish.
Gibson charged extra for a Natural finish. While a sunburst finish could be used to conceal any damage to the spruce top where the binding was added, this wasn’t the case with a Natural finish where immaculately neat, clean edge work was required. As a rule, the company typically set aside premium timber for its Natural finished instruments, where defects in the wood grain would be more apparent.