Blue Diamond Op. 21 is a salon-style work by Jean Eudes Masy that emphasizes melodic lines and expressive phrasing. It is characterized by its sentimental harmonic progression and delicate decorative flourishes.
Students must focus on achieving a beautiful cantabile tone throughout the melodic lines.
Comparable difficulty and character — good candidates for what to learn next.
Blue Diamond (Op.21) is rated Henle level 4 of 9 — intermediate repertoire, roughly ABRSM grades 5–6. In the RCM system it corresponds to about level 5.
You should be comfortable at Henle level 4 — meaning you can already play level 3–4 pieces cleanly. Learning it one level early is possible as a stretch piece, but more than that usually leads to months of frustration.
A typical performance of Blue Diamond (Op.21) lasts about 4 minutes.
Blue Diamond (Op.21) is available as free public-domain sheet music on IMSLP — the score is linked directly from this page.
Pieces at a comparable difficulty and character include Piano Sonata No. 11 in A major by Wolfgang Amadeus Mozart, Andante favori by Ludwig van Beethoven, Belle of the Ball by Leroy Anderson — see the full similar-pieces list on this page.