The Japanese used celluloid for figural parts of mechanical toys and for stand-alone figures, baby rattles and roly polys starting in the early part of the 20th century. Japanese celluloid toys and figures are amazingly resilient considering how delicate the material is. This early plastic is highly flamable and thin enough to be vulnerable to cracking and denting. The thickness of the material varies but in general Japanese celluloid is lighter than that produced by other countries ( the USA, France, Germany or Russia for example). I am constantly amazed by how much is still out there. Sometime in the late 1940's or early 1950's manufacturers had to bow to safety concerns and celluloid was replaced first by acetiloid (often identified with the marketing phrase"inflamable"), and in the case of USA manufacturers like Irwin by viscoloid and then hard plastic, all so that little Johnny could avoid creating an explosion while playing near an open flame.
Pre-War celluloid can often be identified by a small paper label that indicated the item passed inspection or by the company logo (CK for example) cast into the figure, but the 1920's and 30's style of dress, especially on the figures is a reliable indicator. Celluloid was still being used during the Occupied Japan period and the words Made in Occupied Japan were either cast into the celluloid or a paper label or ink stamp was used to mark the piece. After this period true celluloid dissappeared to be replaced by the safer materials.
Celluloid could be either hand painted with a lacquer wash or the color could be imbued in the material. Most toys and figures had a combination of both with the details always being painted. So some celluloid parts (balls or tubes or umbrellas) are all one color while a figure will have clothes and facial details painted by hand. Seperate cast parts could be attached with a solvent which would cause the celluloid to melt slightly and fuse together creating more intricate shapes that would not be able to be cast in one piece.These seams sometimes seperate with age and that is a defect which will be noted but the seams themselves are original. Mechanisms could be placed inside two celluloid halves of a toy in this way although most mechanisms I have seen were inserted through the bottom of the toy. Arms and legs could also be attached to a figure with elastic cording threaded through holes in the body. Thus you will see a lot of celluloid figures with arms and legs hanging loose because the elastic has aged and lost its stretchability. Fixing this by replacing the elastic is about the only repair I usually do since it is easy to do in exactly the same way as the original manufacturer.