Stamps that appear to have no grill
The stamps were issued in 1869 with a grill pressed into the stamp. This is now called the 'G" grill, an illustration and its measurements are seen above. The grills are rarely faked as the stamps without grills are more valuable. The stamps without grills were issued in limited quantities in 1875 and are quite rare today.
Unfortunately for the collector, the grills that were pressed into the stamps were sometimes very lightly pressed giving a very faint grill. The reverse of the stamp has to be examined closely to look for the slightest evidence of a grill or bit of a grill. Dipping the stamp in watermark fluid aids the process.
To complicate matters, on stamps without gum on the reverse it is not that difficult to wet a grilled stamp and press the grill out, thereby making it look like a more valuable ungrilled stamp.
If you believe you have a stamp without a grill then it will only gain value once it has been certificated as such. Beware of buying any stamp without a grill without an accompanying certificate.