Say you go to black-tie parties several times a month. Inevitably, in memory’s haze, they start to blend together – the up-dos, the unidentifiable hors d’oeuvres, the din of chatter.

In that whirlwind of affluence and conviviality, the Frick Collection’s Spring Party stands apart, not as the most hyped party of the year, with all its beautiful people and celebrities, but as the most un-hyped party of the year, with an eclectic crowd of people who truly appreciate the chance to spend an evening in Henry Clay Frick’s Fifth Avenue mansion.

Many of the 440 guests described the party as “low-key,” though the dress was formal, the setting grand, the champagne and brandy the best money can buy.

What created such a relaxed atmosphere? One reason: The party was free.The Frick Collection has held it annually since 1972 to thank its Fellows and Young Fellows for their monetary support – Fellows contribute $1,000 annually; Young Fellows, $500 annually; in both cases, the fee includes privileges for two.

The time of year is also relevant. The party is held in May, perhaps the loveliest month for sipping cocktails in the Frick’s two gardens: the intimate space facing 70th Street, with a koi pool, and the formal lawn facing Central Park.

The timing and structure of the evening were also part of the story.The party started at nine and ended promptly at midnight.The late hour enabled some social jet-setters to attend other events first. A New York City Ballet dancer, Tom Gold, came from a party for William Ivey Long at the Central Park Boathouse, for example, while Christine and Stephen Schwarzman – he’s a newly elected trustee of the Frick – came from American Ballet Theatre’s gala.

With no set time for supper and no formal program, guests filtered in and out as they pleased.The lucky devils had the run of the place: the galleries, with free audio guides; the interior Garden Court; the Music Room, where Peter Duchin got people dancing, and, most exclusive of all, the Director’s Dining Room on the second floor.

The Director’s Dining Room is one room today with a sitting and dining area. Originally it was two bedrooms, for Frick and his sister. The room is not open to the public, so it was quite the treat to lounge there and view the art. Near the dining table hangs Romney’s “Miss Finch-Hatton.” Above the sofa are J.B. Pater’s “Italian Comedians” and “Village Orchestra.” Corot’s “The Pond” is near the door.

Even the trip to the dining room offered a rare sight: On the side of the Grand Staircase, usually blocked with a velvet rope, is the aeolian pipe organ installed in 1914 when the house was constructed. It is one of the largest residential organs on the East Coast. Frick had a salaried organist, Archer Gibson, live in the house.

But organ music would have been too fussy for this affair. So while the organ works today and is regularly tuned, it was up to a jazz trio on the top landing of the staircase to provide the mood music. Michael Gold played string bass, Chris Bergson guitar, and Drori Mondlak percussion.

Love was in the air. Jon Kully and Andie Woloszyn surveyed the Garden Court, where they will have their wedding reception in three weeks (the ceremony will be in the Conservatory Garden in Central Park). The two were joined by the friends who introduced them, Mick and Christine Walsdorf. Another couple recently became engaged: Umit Singh Dhuga beamed at his fiancee, Rachel Sophia Avery Massey.

Two late arrivals at the party plopped themselves down on the steps of the 70th Street Garden: Mr. Gold and friends brought the two pink-clad beauties from the party for Mr. Long. They were Barbie-sized dolls, actually, girls from the Broadway show “Crazy For You,” for which Mr. Long designed the costumes. At his party the girls sat on the dining tables. How quickly they moved up in the world.