From 1930 to1937 Swiss Post issued a set of 7 stamps which were known as the Grilled Gum Stamps. The vertical and horizontal grid points can be seen from the back of the stamp, with or without magnification.

In reality, it was actually the paper that was grilled during the gumming process to prevent the stamps from curling when stored. The grilled gum gives the front of the stamp a brighter and shinier appearance than the stamps that do not have grilled gum.

A good set to look for is the 1933-37 set of seven airmail stamps with grilled gum. However, before buying one must adhere to the detailed inspection of the stamps as some collectors confuse stamps on regular paper with normal slight gum cracking with true grilled gum examples. These stamps might cost you USD 40.75 in unused hinged condition and USD 80 in mint never hinged condition.

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