Cylinders & Plates

Margins. That’s where you’ll find cylinder or plate numbers – unless trimmed off. Made originally by printers to avoid blunders, the inclusion of cylinder or plate numbers (plus traffic lights and various other marginal markings) is now often demanded by Post Offices worldwide to satisfy collector interest. While cylinder and plate numbers are useful during pre-production to ensure everything is in the correct order and the correct place, they’re also useful post-production for quality control (like registration and ink consistency). 

Cylinder or plate numbers are usually collected in blocks as they tend to span several stamps and display better as blocks rather than marginal strips or singles. Historically this was to ensure there was enough selvedge to include a representative sample of the perforation type. The size of block depends on how many stamps the cylinder or plate numbers span. Typical block sizes are four, six, eight and nine stamps, but anything is acceptable so long as all the information is present.

The difference between a cylinder and plate number is down to the printing process. Printing plates are flat while cylinders are cylindrical. Litho, recess and letterpress printing processes use plates. Usually. Gravure printing processes use cylinders. Usually. Suffice to say modern printing techniques blur the lines.

Stamps are normally printed using only cylinders or only plates. This is often due to the choice of printer, printing process, budget or preferred finish. In very rare circumstances printing processes might be mixed. But it's avoided as mistakes are more likely and costs are higher.

Initially cylinder and plate numbers were just that: numbers. The advent of multi-pane and multi-coloured printing meant numbers alone weren’t sufficient to convey all the information. Which is why cylinders and plates are generally alphanumeric. But it's not worth arguing semantics. They are universally referred to as cylinder and plate numbers.

It’s often possible to tell at a glance what are cylinder numbers and what are plate numbers, but it does help to know the conventions different printers use. Just bear in mind printers will sometimes, for no particular reason, do things differently on certain issues.

Cylinder and plate numbers can tell you much about a printing – the colours used, the printing sequence, the quantity of panes, the revision numbers. At a stretch it’s even possible to determine the printer and printing method. All that from a string of alphanumerics. It’s because of the information they proffer that cylinder and plate blocks are highly collectable. Even a dowdy cylinder or plate block will fetch a healthy multiple over a block from elsewhere on a sheet. It’s logical, then, why cylinder and plate blocks of rare printings are highly sought after and command even greater premiums. And completely understandable why varieties within cylinder or plate blocks are considered the ultimate proving pieces.

• A cylinder 3. block printed by Harrison offering three pieces of information – the cylinder revision number, the colour (the same as that used for the printing of the stamps), and the dot indicating the stamps were printed in sheets comprising two panes (one side with dot and the other without)

• Printed by De La Rue, the plate numbers are in the colours used to print the stamps. The stamps were printed in sheets comprising three panes of 60. The letters after the numbers being the pane indicator (in this case being either A, B or C) 

• The 4m History definitive of 1973 was printed by Printex in sheets of four panes of 50 stamps. The panes are differentiated by the letters A, B, C or D after the plate numbers. There should be five plate numbers in the colours of those used to print the stamps. But in this case there are only four because gold is missing...