Embossing, the method used to produce all Government stamped envelopes of the United States and several other countries, is basically letterpress printing. It differs only in that the uninked portions of the printing die are recessed and engraved in design. Under pressure the paper is forced into the recesses and against the engraved design so that the uninked portions of the design are raised above the surface of the paper. For instance, let us imagine that the letter "O" which you are now reading on this page had been printed against a resilent surface so that the center of the "O" would now be raised as you read it. If the pressman handling this particular page has placed a small piece of paper on the cylinder of the press just where this letter appears you will see a suggestion of embossing.

Embossed envelope stamps are, unlike the adhesive stamps we have described at such length, printed one at a time. Each envelope-making machine is equipped with a single printing die. The blanks from which the envelopes are made are cut to shape by means of cutting dies just as your mother or wife cuts out cookies from the rolled dough. These blanks are automatically fed into the envelope-making machine which embosses a stamp at the proper place, gums the flaps, folds and seals the envelope, dries the gum and counts the finished envelopes into any desired number. An ordinary box of five hundred United States envelopes is usually divided into groups of one hundred. This division is done automatically by the machine making them.

Envelope-making machine
The O'Connell Envelope-making machine being demonstrated at an International Philatelic Exhibition in New York.

The making of an embossed die for printing our envelope stamps closely resembles the process we have described for the making of a steel-engraved printing plate. The process differs only slightly and then only in technique. The engraver, as before, cuts the design onto a steel die. In this case the die is the end of a steel shaft. After the die has been made and approved, it is hardened and now is placed directly against a somewhat larger steel shaft. Under very great pressure the hard die is forced directly against the softer steel "hub." As a considerable amount of steel has to be displaced the process requires several applications of the die to the hub. Between each application some of the displaced metal is removed from the hub. When the die has been sunk into the hub to its required depth, the hub is hardened and now, by reversing the process, is capable of striking off as many working dies as may be required.

It will be seen at once that the working die is, in all respects, similar in function to the steel printing plate and performs the same function - namely to print stamps. It differs only in that the working die consists of a single design whereas the printing plate has many subjects. After proper hardening the working die is placed in the printing press, or envelope-making machine. Directly opposite the die there is a resilient substance, such as leather, against which the die strikes. The surface of the die is inked, the paper placed between it and the resilient tympan, and the operation of printing and embossing is completed when the press strikes against the tympan. This striking can be either by direct downward or upward pressure or by a rotary motion. In any case the pressure is sufficient to force the paper hard enough against the engraved recesses of the die to transfer these lines to the paper. The process varies somewhat according to the different machines that may be used. The flat-bed machines usually perform all of the work described excepting only the cutting of the blanks which are always prepared ahead of time. The rotary machines usually perform only the printing of the stamp while the folding is done on other machines. Either flat-bed or rotary machines are capable of printing both the stamp and the corner card in the same operation, there being separate ink fountains provided for the different colored inks. Quite obviously the constant striking of the printing die against the tympan will in time cause the die to wear and will also wear down the tympan. The resulting stamps will, therefore, show some differences which are often startling. While in general and as long as the printing dies are in good condition and kept clean, each embossed stamp on an envelope will be an identical twin to the original die, this is not necessarily so.

effect on stamp
Showing effect on stamp when a letter of the printing die fills up with lint or foreign substance. Letter "U" of "United" has disappeared. When operator cleans die the "V" will again appear on all stamps printed from this die.

The uncolored portions of the printing die are recesses and do not receive ink. However, if some foreign substance, such as lint or dust, should fill up one of these recesses, that particular portion of the die would receive ink and the resulting stamp would be minus a letter or so. Hence we find some envelope stamps on which the letter "U" of ' United" is completely missing. Such missing letters are the result of the die becoming clogged at this point. All succeeding stamps printed from this die in this condition will continue to show the missing letter until the stoppage in the recess either falls out of its own accord or the flaw is noted and the die cleaned. Once cleaned the die will produce perfect stamps. Missing letters such as we have mentioned are much sought after by collectors. The remarkable thing is that so few of them turn up, for the machines making envelopes pound away at the rate of from eight to ten thousand impressions per hour. Naturally enough, also, the forcing of the paper into the crevices of the die will sometimes cause wrinkles and pinches in the paper. Such things are usually ignored by collectors as they are merely characteristic of this method of printing; they are variations that could and do happen at any time without intent or cause.