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What is a plate block?

It's a block of stamps that still has the sheet margin attached, with the plate number printed on that margin. The number identifies the printing plate used, which is why collectors keep the block intact.

Sheets were printed from numbered plates, and the number appears in the selvage, the blank paper around the stamps. Tear the selvage off and it's an ordinary block. Keep it, and it's a plate block, a collecting speciality of its own, particularly in the United States.

Other margin markings are collected the same way: copyright blocks, “Mr. ZIP” blocks and, on coils, plate number singles or strips cut from the roll.

How do I know if I have a plate block?

Look at the margin attached to the block. If it shows a number, usually small and printed near the corner, and the stamps are still joined to it, you have a plate block.

• Modern US issues: a block of 4 stamps with the plate number in the corner selvage.
• Older flat-plate issues: the standard collecting unit is often a block of 6, and sometimes larger.
• Position matters: the selvage should be the one bearing the number, not a blank margin from elsewhere on the sheet.
• Don't trim it. Cutting the selvage down to “tidy” it removes the point of the block.

What are plate blocks worth?

Modern plate blocks usually sell for around the face value of the stamps in them. Classic plate blocks, especially from before about 1940, can be worth several times the price of the same stamps as singles.

The pattern is the same one that governs the rest of the hobby: things collectors deliberately saved in bulk stay cheap. See commemorative stamps value.

What condition issues matter for plate blocks?

Centering across all the stamps, intact perforations between them, clean and uncreased selvage, and gum that has never been hinged. A hinge mark on the selvage alone reduces the price.

• Never hinged is the standard for modern plate blocks. Hinging, even on the margin, cuts value.
• Separation matters: pulled perforations between two stamps devalue the whole block.
• Selvage damage, such as creases, tears and mounting marks, counts against it.
• Even centering across four or six stamps is harder to find than on a single, which is part of the appeal.

See stamp condition grades for the terms dealers use when describing blocks.

Should I break a plate block into singles?

Usually not. A classic plate block is worth more intact than as separate stamps, and breaking it is irreversible. For common modern blocks it makes little difference, since both are worth about face value.

If you're not sure which you have, treat the block as intact until it's been identified. The same rule applies to other multiples: pairs proving an imperforate error, blocks showing a plate flaw, and se-tenant strips are all worth more whole. See error stamps worth money.

What are copyright blocks, ZIP blocks and plate number coils?

They're the other margin-marking collectables. Copyright blocks show the postal service's copyright notice, ZIP blocks show the “Mr. ZIP” reminder, and plate number coils are coil stamps carrying a small plate number on the stamp itself.

Most of these sell for around face value, with the same exception as plate blocks: scarce plate numbers and short-run printings carry a premium, and specialists track exactly which numbers are hard to find. If you're sorting a modern accumulation, don't tear margins off anything until you know which markings it carries.