The first tests are carried out with the A Grill in 1867. The tests are promising, but the A Grill covers the entire surface of the stamp, which reduces the production yield due to an excessive mechanical stress.
The B Grill is an experimental or involuntary aberration. Used in 1868 during the phase of removal of the A Grill, it was too large against the new specified standard that was the F Grill. The four known stamps with a B Grill are 3 cents. They were circulated on a single cover in February 1869 and discovered in 1969. They have been detached later.
The 1868 Z Grill is common for some stamp values but very rare for 1 cent, 10 cents and 15 cents for which it had not been planned, probably for reasons of production sequence.
The 1 cent Z Grill is known in two examples only. Only one of them is remaining in private hands. In a nice freshness, it was sold for $ 965K including premium by Robert A. Siegel in October 1998. This result is still now announced on the site of the auction house as the world record for a used US stamp.
The sale by Robert A. Siegel on June 25 in New York offers three grilled stamps among the rarest variants. Lot 3101 is one of eight known copies of the 30 cents A Grill. Lot 3102 is one of the four 3 cents B Grill discussed above. Lot 3103 is a beautiful specimen of 10 cents Z Grill, from six recorded units. The catalog value of these three stamps is respectively $ 210K, 1M and 650K.
Results before fees :
3 cents B Grill : $ 575K
10 cents Z Grill : $ 325K