Separating stamps from imperforate sheets was cumbersome in poorly lit post offices (hence many imperforate stamps have poor margins). Henry Archer experimented with perforating machines and was granted a patent on the process. The trials were official and he was provided with sheets of stamps for his trials. Most of these sheets were then sent to post offices for use by the public. As previously mentioned, the complete list of plates used is still unclear but most plates between 92 and 101 were used and a few later plates. These plates all have alphabet 1 check letters unlike the 'officially perforated' stamps which are from alphabet 2.
Officially perforated stamps commence at Plate 155 and from here we have a group of plates from which both imperforate and perforated stamps can be found. It is interesting to match perforated and imperforate stamps with the same lettering from the same plate. These are generally referred to as 'matched pairs'.
In this group, some plates are more common imperforate and some more common with perforations. The last few plates issued as imperforate stamps are very difficult to find. The last officially imperforate plate was 177 and imperforate stamps are scarce. Of course, errors do occur (and still do today) and so very occasionally an imperforate stamp can be found from a later plate.
This group of perforated stamps runs from Plate 155 up to Plate 204 and the six reserve plates, R1 to R6. This group is not easy to plate and reference to the imprimatur sheets is recommended. These plates are also covered in the volumes by Fisher and Statham, previously referred to.
Initially perforation 16 was used (C1), but this was not ideal as the perforation holes were very close, so that stamps tended to separate themselves. To overcome this perforation 14 (C2) was phased in. The first plate found with perf 14 is 194 and the remaining plates (except 199) can all be found in both perforation 14 and 16. Once again it is interesting to find matching pairs of stamps.
So far we have not talked about colours and shades. The C1 and C2 issues are the first ones listed by SG with a large range of shades and with a great variation in price! There is clearly a great variety of shades with these issues but oxidisation can also cause colours to darken. Identification of the rare plum shades is difficult and stamps with certificates from the authentication bodies are preferable.