The Code Page Was A Photographic Plate Negative
Photographic plates turn out as negative in the first instance and the code page is an image of the negative plate that was used.
Below you will see the image of a photographic plate, notice how light in colour and how detailed the left hand side and lower central area of the image is. All that was dark is turned a lighter colour and all that was light has become a darker colour:
What this means is that the micro writing was:
1. Photographed and processed using the photographic plate method
2. Which captured and displayed extremely fine detail for the image
3. Then highlighted the lighter coloured indentations on the page
4. Which became a darker colour in the image we now see as the Somerton Man code page.
5. The end results are the micro letters and numbers that were discovered and shown here by the author of this blog.
You can verify this with an expert in Police Photography methods of the 1940s.