The original format in which stamps were issued was full sheets. As time went on, postal authorities began to produce stamps for sale in more convenient formats for postal users. In the era before postage meters (and now, pre-printed postage indices), coil stamps were issued as the preferred method of stamp purchases for large mailing houses. Issued in rolls (sometimes up to as many as 10,000 in a single roll), the mailing houses could place these large rolls in their mailing machines and lower their labor costs as these stamps were automatically affixed. Individuals could buy coils, too (and some countries, such as Sweden largely had coils as their preferred method of stamp production), but for the most part coils were produced mainly for business use.
Booklets represented a tremendous innovation in stamp design and sales, and were arguably the most consumer friendly innovation since the introduction of perforations in 1851. Stamps are small, perishable pieces of paper that stick together or to other surfaces unless handled carefully. As populations became more mobile and postal use more pervasive, there was demand for stamps that could be safely carried in pockets or purses to facilitate mailing on the go. Let’s remember that in 1900 most big American cities had three mail deliveries a day and postal boxes on every corner. There was no real telephone service yet and people wrote notes constantly. Stamp booklets solved the problem of keeping mint postage stamps undamaged with gum intact for use by active people. First issued by the United States in 1901, the earliest stamp booklets were very simple- just two panes of six stamps stapled between cardboard covers with some glassine interleaving between the panes to keep them from sticking together.
The first collectors of booklets and booklet panes didn’t know how to collect them, how to store them, or in what formats later collectors were going to want them. Therefore, many early collectors damaged the booklets that they tried to save. At first, collectors didn’t really see that booklets were their own collectible variety. After all, they looked like the real stamps, just issued in blocks of six. But the printing and perforating process for booklet stamps are different and there are subtle design and size differences on many of them. The imperf sides of the booklet stamps soon led collectors to place them in their collections as separate items from the original stamps. Colleectors simply detached the panes from the booklets, leaving the pane without the tiny selvage into which the little staple ran that was used to fasten it to the booklet. Today, panes without these selvages are considered damaged and are not desired by collectors.
Perhaps the biggest change in booklet and booklet pane collecting in the last thirty years is the relative increase in complete booklet collecting at the expense of simple pane collecting. The first booklet panes were very simple- just two identical panes stapled into a simple booklet with a cover. As booklets got more complex, with multiple panes of different denominations, collecting the entire booklets became more appealing. And, today, booklets are all self adhesive, making the pane and the booklet identical.