Originally published in 1975,  The Bear Detectives was part of Random House’s Beginner Books series.  Jan and Stan’s art file for this book has a number of things of interest.

The cover went through a several drafts before the final art work was determined.

All Berenstain Bears books begin with pencil sketches.  These are the sketches for the first 2 pages in the book:

Here are those pages as they appeared in the printed book:

In the early days of the Berenstain Bears books, they were printed by color separation.  In this process the original artwork is separated into individual color components for printing. The components are cyan (blue), magenta (red), yellow and black, known as CMYK. By combining these colors, a wide spectrum of colors can be produced on the printed page.  Each color is printed separately.  When the colors are combined on the paper, your eye combines the colors to see the final image.

To create a piece of color art by this process, the artist had to first complete a line drawing in black ink.  This drawing was then printed on four separate pieces of illustration board in light blue.  Photographic film was not sensitive to this tone.  A similar principle was used in the “blue screen” process for special effects in films.  The artist then painted gray washes on the four pieces of board.  The darkness of the wash determined the darkness of each color.  A gray-percentage chart was provided as a guide.  Equivalent shades of gray and color were shown so the artist could judge how dark the gray tone should be.  Stan and Jan created all their children’s books, published between 1962 and 1975, by this exacting process.

What follows are the color separated pages that became the finished page at the end.

Remember Stan and Jan had to go through this process for each page in every book they created during that time.