I saw an incomplete version of this film in July 1996 at the Cinema Ritrovato festival in Bologna; they screened a 6-minute fragment (from the archives of Cinematheque Suisse) that had no captions. At the beginning of the fragment is a brief shot of a girl holding a card marked "Entr'acte" ... implying that this surviving fragment is the beginning of the film's second half.
'The Casket of the Rajah' appears to be a trick film similar to what Georges Melies was producing at this time, but with the atmosphere of the Arabian Nights: I was reminded of Raoul Walsh's wonderful 'Thief of Bagdad' film (which I much prefer to the Michael Powell one, even though I'm a fan of Powell).
Judging from this fragment, the entire film seems to be merely a vehicle for illusions and spectacles. An evil magician visits the rajah's palace to perform his magic tricks, but he also steals a valuable casket ... making his getaway aboard a dragon. The rajah pursues the wizard to a subterranean cavern which is full of dancing girls ... well, it would be, wouldn't it?
The magic tricks and the special effects in this 1906 effort are all -- by 21st-century standards -- very crude: the wizard's dragon seen here is much less impressive than the one in Fritz Lang's 'Siegfried' only a few years later. What's truly dazzling (in the print which I viewed) is the spectacular hand-tinting. The film-makers had the sense to use this conservatively in the early sequences. When the wizard's magic flame burns red and yellow, the effect is more impressive because the rest of the frame is monochrome. Later, as the wizard escapes on a green dragon (that breathes red flame), the wizard's robes become yellow and pink. Still later, the dancers' costumes change colour as they whirl like dervishes.
Although I found this extremely impressive, I was aware of the labour behind it. Women and girls were paid a pittance to ruin their eyesight, painstakingly hand-colouring one frame at a time ... taking days and weeks to create an effect which lasts only a few seconds on the screen. But that effect is very impressive indeed. However, since I saw only a brief fragment of this entire film, I shan't rate the movie.