A cardboard box being used by mom for over half-a-century

I noticed this small cardboard box being used by my mom, an octogenarian, to preserve a valuable memory of hers from a long time ago. The box is of W & R Balston Ltd’s Whatman Filter Paper No.1, Made in England.

Searching online I learned that:

1. the design of the box was from the 1950s or earlier;
2. the filter papers were mostly used in chemical processes (maybe we used it when my family #LIFCOBOOKS owned a book printing press in North Arcot District in the 1950s);
3. there are many grades of the filter paper each with a unique number to identify the Particle retention capabilities and the thickness.