It is of crucial importance to be able to correctly identify different types of grills embossed on U.S stamp issues from 1867-1875 in order to distinguish between their possible varieties, as the difference in catalogue value can be immense.

In order to prevent cleaning and reuse of postage stamps U.S. government (Post Office Department) introduced a grilling process in 1867, an invention credited to Charles F. Steel, a supervisor within the National Bank Note Company at the time.

Grill is essentially an embossed impression applied by a roller in order to cause a breaking of fibers in the stamp paper to the extent that when the ink from cancellation soaks inside the “grilled area” of the stamp and gets absorbed into the paper, it inevitably prevents almost any possibility of “cleaning” and reuse of the stamp.

A grill consists of a certain number of parallel rows, with each row being composed of a series of pyramidal shapes called “points”, forming a grid-patterned impression on a stamp. The number of “points” in a row and the number of rows or the area grill covers varies depending on the type of grill.

A photo showing grill i.e. grilled area on 10c George Washington stamp from 1867-1875 issue

In short, classification of grills is based on the area that the grill covers, if the points face upwards or downwards from the face side of the stamp and if the ridges on them are horizontal (only Z grill) or vertical.

Grills that are points-up (A,B and C grills) are found on stamps embossed from the gum side towards the face side of the stamp and where embossing tips (ridges) are visible when looking at the front of the stamp (as the grill points are raised above the front surface of the stamp).

Grills that are points-down (D,E,F,G,H,I,J and Z grills) is embossment from the face side of the stamp towards it’s gum side, with the embossment i.e. ridges being visible at the back of the stamp.

Classification of grills is based on their designation by letters of alphabet raging from A to J, according to the number and type of points/ridges they contain.

Identification of grills as they are denoted by letters of the alphabet:

Ridges are the tips of the pyramidal shapes or more specifically ridges are the junction at the very top of the sides of pyramidal shapes that constitutes the “point” of a grill. On all grills ridges are vertical with the exception of a Z grill, whose ridges are horizontal. For the identification of a grill we can either count the points in a row individually, as well as number of rows, or we can measure the area of the grill it covers on a stamp.

Peculiarity of a Z grill is that its pattern has horizontal ridges incised into the stamp paper whereas all other grill patterns have vertically incised ridges.

Vertical ridge vs. horizontal ridge

Also, certain Z grilled stamps i.e. 1 cent B. Franklin, 10 cent G. Washington and 15 cent A. Lincoln stamps with Z grills from 1868 due to being a very short time in production made them one of the rarest U.S. stamps.

Not all grill patterns were used on each denomination of a stamp making certain combinations of particular stamp and grill occurring very rarely.

While some stamps with grills are fairly common, others can be relatively rare and valuable. In some instances, very few copies remain of certain stamp/grill combinations as is with the case of some of the most rare and expensive U.S. stamps in existence.

For example, ranking among the most valuable U.S. stamps are grilled issues from 1867/68 i.e. 1 cent Benjamin Franklin, 10 cent George Washington and 15 cent Abraham Lincoln stamps with Z grills, 3 cent George Washington B grill, 5 cent Thomas Jefferson A grill stamp etc.

It is of utmost importance to be able to correctly identify the grill on a stamp as only subtle difference between grill characteristics can make enormous difference in terms of a value of a stamp.

In order to properly identify the grill/stamp very convenient tool for fast and accurate measurement is the Sonic Imagery Labs Precision U.S. Speciality Multi-Gauge. It is comprised of 12 different measuring devices that enable easy and correct identification of most notably early issues of U.S. stamps.