STEPHEN McGuinness of Plum Blossoms came face to face with greatness this week and was flabbergasted. ''I've only ever seen Rembrandt's etchings blown-up, so I was amazed to find most of them are small - more or less in the range of baseball cards. ''Of course that makes them all the more exquisite. Fantastic detail.'' How did the boss of the popular gallery in Exchange Square come to make this discovery? By expanding his hitherto Asian art operation into the international arena - and starting off with the really big time. Showing at Plum Blossoms from April 22 to May 1 will be The Etchings of Rembrandt, featuring 40 works by the 17th century Dutch master. It's an unprecedented event for Hongkong and has come about thanks to McGuinness' association with Galerie Michael of Los Angeles, whose collaborators include one of the world's authorities on Rembrandt's etchings. As a result, Galerie Michael tends to get first pick when important pieces come on the market and its fine collection is now being offered for sale at selected galleries including Plum Blossoms. Rembrandt Harmensz Van Rijn was in his early 20s when he etched his first copperplate and continued to produce plates until 10 years before his death in 1669. Notes Plum Blossoms: ''Some art historians have gone so far as to suggest that his etchings surpass his paintings in greatness.'' Included among the 40 at Plum Blossoms will be the only known counterproof of Rembrandt's Adam and Eve. Prices will range from $25,000 to $575,000. COMING soon to the Hongkong Museum of Art will be an exhibition devoted to another great master: Auguste Rodin (1840-1917). Fifty-seven original bronzes by the Frenchmen known as the father of modern sculpture will be on display from April 30 to June 2 thanks to the Urban Council and France's Ministry of Foreign Affairs. In honour of the event, a seminar (May 15) will be conducted by local and overseas experts including leading authority on Rodin, Professor Ruth Butler of the University of Massachusetts, and local sculptor and museum adviser Van Lau. A special ''Rodin pass'' is now on sale at the Museum of Art. Costing just $20, it will assure you of a reserved seat at the seminar and comes with two entry tickets valid for the entire period of the exhibition. Unbeatable value, but don't delay. It's first come, first served. LAST December saw Hongkong's introduction to some of Ireland's brightest young talents including Maurice Quillinan who worked with Henry Moore before setting aside sculpture and turning to painting and drawing. Quillinan is now back for a new exhibition - this one featuring six other leading sculptors and painters. Presented by Arts 'n' Noise at the Excelsior Hotel Grill for two weeks starting tomorrow, Seven Irish Artists in Hongkong will comprise an all-male lineup. The common denominator for David Dunne, Eamon Colman, Aidan Gaffney, Paddy Lennon, William Thomas, T.J. Maher and Maurice Quillinan is that all have been given a platform by Dublin's Pantheon Gallery, set up in 1991 to promote the country's most outstanding young artists. SCHOENI Art Gallery got off to an impressive start last month with an inaugural exhibition which included fast-rising Chinese star Liu Dahong. Now this specialist in contemporary Chinese and Western art is focusing on individual talents, starting with Russian painter Vladimir Kush. '' . . . my art seeks to articulate complex layers of meaning, a brilliant and concise fusion of paradox,'' says the prize-winning artist who was trained at Moscow's Strogonoff Art Institute and enjoys an international reputation. Accordingly, Kush has titled his show at Schoeni (On Hong Building, Central) Ambiguous Visions, though the painting featured on the invitation is far from obscure - five voluptuous naked females. Also showing is Wong Kee-chee whose latest oils can be seen at the Trigram Gallery, Kowloon Hotel, from today until May 3 and New Hope, New Horizons, an exhibition of recent art from Vietnam being presented by Asian Horizons at Artpreciation, Stanley Street, Central, until May 8.