Essed lowered his nose to the guitar’s sound hole and inhaled. The purpose was practical rather than spiritual: If the Euphonon had been repaired recently, he explained, the glue would give off a telltale odor. As Essed put it, an old guitar should have a scent “like grandmother’s attic” if it hasn’t been worked on in the recent past. That observation caused his boss, Retrofret owner Steve Uhrik, to muse on the glues used in antique guitars, which he says were rendered from horses or rabbits.

Call it the intersection of the sacred — and the earthy. Inside that Manhattan warehouse is the vast majority of a collection of 265 rare guitars that will go on auction on April 2 and 3 in New York. Dubbed “The Artistry of the Guitar,” it includes showstoppers such as a 1930 Martin OM-45 Deluxe — one of only 14 ever made — an 1862 Antonio de Torres classical model, and coveted archtops made by the legendary John D’Angelico. Other makers range from Arcangel to Epiphone to Prairie State to Stromberg to Washburn to Weissenborn. A handful have a celebrity provenance — a 1941 Gibson SJ-200 once owned by Stephen Stills stands out — but in large part the instruments themselves will be the stars of this show.

The sale is being conducted by Guernsey’s, which has experience in what musicians might consider holy relics. In 2005, for example, it auctioned John Coltrane’s tenor saxophone, Charlie Parker’s alto, one of Dizzy Gillespie’s famously angled trumpets, and a clarinet of Benny Goodman’s. Before that, Guernsey’s also offered two custom-made electric guitars (the “Tiger” and the “Wolf”) built for the late Jerry Garcia. Arlan Ettinger, who co-founded Guernsey’s with his wife Barbara Mintz, describes “Wall Street types coming to the previews of the Garcia show and getting down on all fours to look” at Tiger and Wolf through the glass showcase windows. Some, he says, asked to touch the instruments and, when granted permission, kissed them reverently. (Ettinger and Mintz both come from the advertising world, and Ettinger contends that Guernsey’s stands out among much larger rivals for its marketing pizzazz and its ability to infuse a sense of story into a collection. Other marquee auctions handled by their firm have included documents, artifacts, and memorabilia relating to John F. Kennedy, Elvis Presley, Mickey Mantle, as well as Mark McGwire’s 70th home run ball.)

Fortune was offered a sneak peek at Guernsey’s stunning guitar collection, and since our enthusiasm for the instruments far exceeds our knowledge and acumen, we invited Essed and Uhrik to join us as expert guides. Click through the gallery to see and read about some of their favorites, along with several other notables.

1934 Euphonon

"What a guitar," Uhrik gushed. "For me this is a standout piece." It's not the fanciest, he added (though the instrument has some graceful abalone trim), but it's "just amazing." He praised its sound, but was quick to acknowledge that many collectors have no intention of playing instruments they acquire. As he put it, "no one invests in a stamp collection because they want to mail a letter." Euphonon was one of multiple brands, including Prairie State and Stahl, for whom two Swedish-immigrant brothers, Carl and August Larson, made guitars in Chicago in the 1930s and 1940s.

1929 Gibson HG-24

The HG-24, according to Uhrik, embodies two trends of its era: First, the popularity of Hawaiian music (the "HG" in the name stands for "Hawaiian guitar"), which was one of a number of factors driving the widespread adoption of metal strings; and second, the need for guitars to try to produce more volume, as they sought to be heard in ever bigger and louder bands. (Electric models began to take hold only in the 1930s.) The HG-24 actually has, as Uhrik puts it, "a body inside a body." The makers were trying to make use of a phenomenon called "Helmholtz resonance" to try to generate more sound. Uhrik says the HG-24 "did not take off" and noted that it was discontinued in 1931. But he credited it for some "significant innovations," such as the fact that it was the first of its size and shape to have a neck attached at the fourteenth fret. "This is a very, very rare guitar."

1930 Martin OM-45 Deluxe

The OM-45 Deluxe was Martin's crown jewel in the 1930s, and the company made only 14. Each sold for a princely $225 at a time when the company's least expensive guitar went for $5. Another Deluxe -- one that belonged to the late Roy Rogers --sold for $460,000 at a 2009 auction. This one doesn't claim past celebrity ownership, but it's expected to be a highlight of Guernsey's auction. The OM-45 Deluxe is known both for the beauty of its sound and the elegance of its ornamentation, viewed by some as the most desirable instrument ever sold by the Cadillac of guitar-makers.

1935 Gibson Super 400 Flattop Custom

Uhrik has an acronym for guitars this rare: "GFA:" "Go find another." As he puts it, "this is a 'wow' guitar." It's made for Hawaiian-style music. Though not visible in the photograph, the frets do not rise above the fingerboard and the strings are kept high. It's meant to be played on one's lap with a slide.

Late 1930s Larson Hispana

Uhrik gasped when the case was opened to reveal this marvel. Essed praised its "almost Shaker" aesthetic. The Larsons who designed it are the same brothers who crafted instruments for Euphonon, Prairie State, and others. It has a "floating bridge," which is common among archtops (as well as standard for violins and cellos), but unusual in a flattop guitar with a fixed tailpiece. (The bridge is what raises the strings to playing height and, in this case, "floating" refers to the fact that the bridge is not glued or otherwise permanently attached to the instrument.) The design was rare enough that U.S. patent #2,208,391 was procured for it. As the patent application stated, "It is an object of the invention to attain greater beauty and fullness of tone by inducing vibration of the sound board in a different and amplified degree compared with that vibration which is induced in guitars of the known construction."

1920s Stella Auditorium 12-string

Connoisseurs sometimes joke, according to the Retrofret experts, that Stella guitars are "packing crates with strings." They were built from inexpensive materials but produce a powerful sound. That's why some of the most famous blues and ragtime players -- including Lead Belly, Blind Willie McTell, and Blind Lemon Jefferson -- used models like this one. In the early 20th century, when guitarists sometimes tried to sound like pianos, this instrument delivered a big tone, and its 12 strings gave it the ring of a barrelhouse piano.

1941 Gibson SJ-200

According to Guernsey's, Stephen Stills strummed this six-string (along with numerous Martins) during his days with Crosby, Stills, Nash & Young in the early 1970s. The company made only 100 SJ-200s with backs made of East Indian Rosewood, according to the catalog, making this model all the harder to find.

1936 D'Angelico Style A

John D'Angelico had been running his own shop on Manhattan's Lower East Side for only a few years and was still emulating Gibson's L-5 when he constructed this archtop, according to Uhrik. "This was his first model," he says (though Uhrik adds that the luthier had already begun adding his own embellishments). Over three decades, D'Angelico would hone an exquisite personal style, and his little shop hand-made about 1,100 archtops (many of them tailored for specific buyers) that were particularly sought-after in New York jazz circles.