Editing Envelope (section)

==Overview==
[[File:USPatent701839-CallahanAmericus-WindowedEnvelope.gif|thumb|[[Patent drawing]] of [[Americus Callahan]]'s windowed envelope]]
A folding sequence such that the last flap closed is on a short side is referred to in commercial envelope [[#Manufacture|manufacture]] as a '''pocket''' – a format frequently employed in the [[packaging]] of small quantities of seeds. Although in principle the flaps can be held in place by securing the topmost flap at a single point (for example with a wax seal), generally they are pasted or gummed together at the overlaps. They are most commonly used for enclosing and sending [[mail]] ([[letter (message)|letters]]) through a prepaid-postage [[postal system]].

'''Window envelopes''' have a hole cut in the front side that allows the paper within to be seen.<ref>{{cite web|title=History of Envelopes|url=https://www.businessenvelopes.com/history-of-envelopes-c-111.html|publisher=BE|access-date=27 December 2014|quote=Window envelopes have a small plastic pane that fits an address printed onto the letter inside. Windowed envelopes soon became the standard for business envelopes, as they reduce the time and cost required to send mail while still ensuring it gets delivered to its intended destination.}}</ref> They are generally arranged so that the receiving address printed on the letter is visible, saving duplication of the address on the envelope itself. The window is normally covered with a transparent or translucent film to protect the letter inside, as was first designed by [[Americus Callahan|Americus F. Callahan]] in 1901 and patented the following year.<ref>{{cite web|title=US 701839 A|url=https://patents.google.com/patent/US701839|access-date=27 December 2014}}</ref> In some cases, shortages of materials or the need to economize resulted in envelopes that had no film covering the window.{{citation needed|date=December 2014}} One innovative process, invented in Europe about 1905, involved using hot oil to saturate the area of the envelope where the address would appear.{{citation needed|date=November 2020}} The treated area became sufficiently translucent for the address to be readable. {{As of|2009}} there is no international standard for window envelopes, but some countries, including [[Germany]] and the [[United Kingdom]], have national standards.<ref>{{Cite web |url=http://www.belightsoft.com/products/companion/paper/envelopes.php |title=A software company's information on US and &#91;&#91;International Organization for Standardization{{!}}ISO&#93;&#93; international standard envelope styles and sizes |access-date=20 November 2009 |archive-url=https://web.archive.org/web/20130531013254/http://www.belightsoft.com/products/companion/paper/envelopes.php |archive-date=31 May 2013 |url-status=dead }}</ref>

An [[aerogram]] is related to a [[letter sheet]], both being designed to have writing on the inside to minimize the weight. Any handmade envelope is effectively a letter sheet because prior to the folding stage it offers the opportunity for writing a message on that area of the sheet that after folding becomes the inside of the face of the envelope. For document security, the letter sheet can be sealed with wax. Another secure form of letter sheet is a [[Letterlocking|locked letter]], that is formed by cutting and folding the sheet in an elaborate way that prevents the letter from being opened without creating obvious damage to the letter/envelope.

[[File:JapaneseFuneralEnvelope.jpg|upright=0.75|thumb|A Japanese funeral envelope used for offering condolence money. The white and black cords represent death. Similar-looking envelopes with red and silver cords are used for weddings.]]

The "envelope" used to launch the [[Uniform Penny Post|Penny Post]] component of the [[United Kingdom|British]] postal reforms of 1840 by [[Rowland Hill (postal reformer)|Sir Rowland Hill]] and the invention of the [[postage stamp]], was a lozenge-shaped lettersheet known as a [[Mulready stationery|Mulready]].<ref>{{cite web |title =Mulready stationery: Lettersheets and envelopes |work =The Queen's Own: Stamps That Changed the World |publisher =[[National Postal Museum]] |url =http://www.postalmuseum.si.edu/queen's/mulreadystationery-list2.html |access-date =25 September 2006 |archive-date =10 December 2019 |archive-url =https://web.archive.org/web/20191210165209/https://postalmuseum.si.edu/queen%27s/mulreadystationery-list2.html |url-status =dead }}</ref> If desired, a separate letter could be enclosed with postage remaining at one penny provided the combined weight did not exceed half an ounce (14&nbsp;grams). This was a legacy of the previous system of calculating postage, which partly depended on the number of sheets of paper used.

During the [[U.S. Civil War]] those in the [[Confederate States Army]] occasionally used envelopes made from wallpaper, due to financial hardship.

A "return envelope" is a pre-addressed, smaller envelope included as the contents of a larger envelope and can be used for courtesy reply mail, [[metered reply mail]], or [[freepost]] (business reply mail). Some envelopes are designed to be reused as the return envelope, saving the expense of including a return envelope in the contents of the original envelope. The [[direct mail]] industry makes extensive use of return envelopes as a response mechanism.

Up until 1840, all envelopes were handmade, each being individually cut to the appropriate shape out of an individual rectangular sheet. In that year George Wilson in the [[United Kingdom]] patented the method of [[tessellating]] (tiling) a number of envelope patterns across and down a large sheet, thereby reducing the overall amount of waste produced per envelope when they were cut out. In 1845 [[Edwin Hill (U.K.)|Edwin Hill]] and [[Warren de la Rue]] obtained a [[patent]] for a [[steam]]-driven machine that not only cut out the envelope shapes but creased and folded them as well. (Mechanised [[postage stamp gum|gumming]] had yet to be devised.) The convenience of the sheets ready cut to shape popularized the use of machine-made envelopes, and the economic significance of the factories that had produced handmade envelopes gradually diminished.

As envelopes are made of paper, they are intrinsically amenable to embellishment with additional graphics and text over and above the necessary postal markings. This is a feature that the [[direct mail]] industry has long taken advantage of—and more recently the [[Mail Art]] movement. Custom printed envelopes has also become an increasingly popular marketing method for [[small business]].

Most of the over 400 billion envelopes of all sizes made worldwide are machine-made.