This is heavily revised and updated version of my original post, with various
corrections and additions made in the light of information received from David Mitchell
and some new detective work of my own. I am most grateful to David for his valuable input.
In issue 320 of the British Origami Society magazine (February 2020) I had an article entitled “Two Early Letterfolds” about folding instructions for two letterfolds in two old German books, Leichte Künsteleien (1819) by Dr Heinrich Rockstroh and Das Buch der Zauberei (1839) by Johann August Donndorff. They were early examples of the use of diagrams to explain paperfolding. A copy of the article is included here.
Since then I've come across another book by Dr Heinrich Rockstroh which again includes the Puzzle Purse, but also another folded paper item also referred to as a letterfold. The book is called Mechanemata oder der Tausendkünstler (1831), and luckily for us it's available in digitised form via Google Books. It’s a large collection of the kinds of tricks, amusements and scientific experiments that were popular at the time, compiled from various sources. “Mechanemata” is Latin for “mechanisms” or “tricks”, and “Tausendkünstler” is a German term for “magician” or someone who is "skilled in many things". There are copperplate illustrations at the end of the book showing some of the items described, including both the letterfolds.
Why "artful letter closures"?
Both letterfolds appear under the heading Künstlicher Zuschluss eines Briefes, which I've translated here as “artful letter closure”. In modern German künstlich normally means "artificial" and often has the same slightly negative connotation as in English, suggesting something unnatural or inauthentic. But from online copies of dictionaries dating back to the mid-19th century it seems that in both languages the usual sense back then was more like that of “artful” or “clever”.
Copperplate illustrations
from Mechanemata (1831)
Mechanemata actually has a lot of interesting material in it, including several of the paper-related tricks I've covered elsewhere in this blog. I hope to look at some of these in future posts, but for now I'll just focus on the two letterfolds, which Rockstroh describes as "artful letter closures".
The Puzzle Purse (page 125)
The written instructions for the Puzzle Purse (page 125) are a little simpler than those found in Rockstroh’s earlier book Leichte Künsteleien, and the diagrams slightly more detailed. This seems to be the source which Donndorff borrowed from for his description and diagrams in Das Buch der Zauberei.
 | An artful letter closure (1) The sheet of paper chosen must be as long as it is wide. You can quickly be sure of this if you fold the sheet so that two initially adjacent edges lie one on top of the other. First fold the sheet, as shown at the top left at 1 on the fourth copper plate, so as to make nine equally sized squares, and also twice so as to produce two creases from one corner to the other or two equally sized triangles each time. All the creases are visible on the side of the sheet with writing on it, and are not raised but indented. Then make a diagonal fold on each of the outer central squares, the same as on the outer square to its left, and so that the paper is folded over and not under as with the previous folds, and therefore these four folds are raised on the side of the sheet with writing on it, not indented like the others. Now, using the outer triangles, try to fold the sheet together so that the surfaces of triangles a and b, triangles c and d, triangles e and f, and triangles g and h lie against each other, and the diagonal folds on the outer central squares lie on the middle of the small inner square, so that the whole thing is as shown at 3 on the left. Now fold the outer triangles over one on top of the other. But slide the last of these triangles underneath so that part of this triangle is itself under the first triangle; in this way when the sheet is properly closed it looks the same on one side as on the other – as at 3 on the top right in the drawing on the same copper plate. |
Nowadays the instructions would be a bit more concise and easier to follow, and would probably look something like this:
The Cross Letterfold (page 267)
I've called this the Cross Letterfold because it's based on an old napkin fold known as: The Cross. To be honest, it's not really very practical as a letterfold, but it would certainly be much more interesting to receive a letter folded like this than just folded in half.
 | An artful letter closure (2) The sheet of paper chosen, as for the artful closure described in the second chapter of this book, must be as long as it is wide. First fold the sheet so that the corners meet in the middle on the side with writing on it, as shown below 1 and 2 on the fourth copper plate; thus so that the corners are folded first over and then under. This folded shape, after turning over, is folded again or as shown by the dotted lines below 1 and 2, and in this way we obtain the folded shape above and to the right of 2. This folded shape, after turning over, is once again folded in the same way or as shown by the dotted lines in the aforementioned drawing, and in this way we obtain the folded shape below and to the right of 2 on the fourth copper plate. By taking any one of corners a, b, c and d and going underneath we now try to raise the triangles sideways and fold them over so that the folded shape is as shown above 4 to the right. Then we fold each of the two small side triangles over and press well down; in this way the folded shape will appear as at 5, but on the other side as at 6, at the bottom on the second copper plate. The middle square on the side at 6 is used to write the address on this artificial letter closure. |
Again, the written instructions are not particularly easy to follow, but the diagrams make it much clearer. First take a square sheet of paper and write a letter on it. Fold the four corners in to the middle (i.e. in origami terms make a "blintz"), then proceed as follows:
The first four diagrams come from Plate 4, but the last two are at the bottom of Plate 2. There are a couple more at the top of Plate 2 that look as if they might be related, but these are actually Klangfiguren or Chladni Figures. If you’ve never heard of Chladni Figures before (as I hadn’t), a quick Google search will reveal all.
More about the Cross fold
The second letterfold in Mechanemata starts out like the traditional Japanese design Yakko San, but then has the small corners folded inwards at the end. At least, that's how I first saw it. I asked David Mitchell, who knows a lot more than I do about early Japanese folding (and for that matter about the history of paperfolding in general) and has a page on his website devoted to Yakko San. He quickly pointed out that the same basic fold was also found in Europe at around the same time, and also even earlier as a napkin fold that goes back at least as far as L'escole parfaite des officiers de bouche (1662) published by Jean Ribou (available on Google Books - see the Croix de Lorraine (Cross of Lorraine) on page 108). An excellent reference work for this and everything else to do with the history of tablecloth and napkin folding is Joan Sallas' Gefaltete Schönheit (originally in German but now also available in English as Folded Beauty).
From L'escole parfaite des officiers de bouche (1662)
The Cross is still found in modern works on napkin folding. But the paper version also appears in a lot of old books under various names and as a starting point for other designs. Friedrich Fröbel included it in his paperfolding work for kindergartens, and the basic form is described in Des Kindes erstes Beschäftigungsbuch (1876) by E. Barth and W. Niederley as a Garnwickel (a "pirn" or yarn holder), with instructions on how it can be developed further to make a jacket and trousers for a kind of paper doll. As it happens, the Puzzle Purse is also in Barth and Niederley, under the title of Couvert or Envelope.
The Cross as a paperfold and a napkin fold in
Des Kindes erstes Beschäftigungsbuch (1876)
by E. Barth and W. Niederley
 |  |
Envelope, paper clothes and furniture from the 5th edition of
Des Kindes erstes Beschäftigungsbuch (1900)
by E. Barth and W. Niederley
An English adaptation of the Barth and Niederley book was published as Pleasant Work for Busy Fingers (1891) by Maggie Brown.
The same basic cross form appears in other early books, including De kleine papierwerkers I (1863) by Elise van Calcar, where it's referred to as an Ink Well, and later on with a few modifications as a Steamboat or Battleship (see David Mitchell's site).
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