Letters and Numbers

An index points. We might think of the index as an outstretched finger directing the way. (This is how the first finger on each hand got its name, the index finger—the one that points, that indicates, makes known). Or, it is a list in the back of a book that directs you to the correct page number to find the information you require. In 19th-century semiotics, philosopher Charles Sanders Peirce sought to formalize a way of thinking about signs as a continuation of his studies in logic. He wrote about the icon, the index, and the symbol. The icon physically resembles the thing it stands for (a small picture of a plane stands in for the plane itself) and the symbol points to connotations (usually word-based, but also in the sense that the bald eagle is also a symbol for the USA). However, the index is a sensory feature that correlates and implies something else. The classic example of an index is the presence of smoke, an index of a nearby fire.[1] Though it may have been unintended in its original design, the rhythmic clacking of the Solari display also has this signifying effect. Its cascade of clicking turns faces upward. The noise of the circulating flaps acts as an index—it points to new departure and arrival information. And maybe this indexical noise can’t be underestimated—when Boston’s Massachusetts Bay Transportation Authority replaced their split-flap displays in 2006 with digital LED displays, they retained the noise of the analog departure board:  a tick-tick-tick emitted by a speaker system inside of the board when the schedule changed over.[2]

In addition to the rustle of letters, there are a few other factors that make the analog split-flaps appealing (aside from retro-nostalgic longing, which is patently undeniable and yet perhaps a whole other story). Unlike digital displays, which become washed out and hard to see in bright light, and can only be read when regarded straight-on, the high contrast white-on-black letters of the Solari display allows for higher visibility in most light conditions. It is also able to be read from many different angles—which is useful in airports and train stations, where people are dispersed across the arrivals and departures area. Additionally, unlike a LED display that must remain lit when it is static, a split-flap display uses very little power until it is instructed to flip. And if power is cut temporarily to the system, the information remains visible instead of falling dark and then resetting in a jumble when the power returns.

Although we’ve delved mostly into the visceral mechanics of wiring and breadboards so far, the flaps themselves are the capricious face of each display. Originally metal and later plastic,[3] they came in the form of a fixed text (the whole name of a station or an airline) or an alphanumeric display that could be programmed individually. They would have been industrially cut and silk-screened in sheets. This was complicated in terms of individual replacements. As Tom Chaffin, the acting Principal Engineer for Telecoms at Thameslink writes of the fixed text displays, “every time the timetable changed altering train service calling points or final destinations changed or even for a train company name/branding change, new flaps had to be silk-screen printed and then inserted into the indicators ideally the night of the timetable change.”[4] With an entire rail or airport system, this process was costly and time-consuming. As a person responsible for the twice-yearly updates for the Southern Regions rail system reminisces, delivery took about 9 months, so you would have to predict requirements a year in advance. However, he notes, they could also order the flaps in multiple colours, and even could use the “rest position” as an advertising display for newspapers and whiskey.[5]

Black and white split flap board showing fixed and alphanumeric flaps from Kagoshi, Japan, small pink flowers in front of it, and airport arrival information on the boards.
Wikimedia Commons, “Split-flap display in Kagoshima airport, Kirishima, Japan.”

We’re working with two arrivals/departures displays—relatively small ones in the grand scheme of the giant multi-city boards Solari has manufactured—each display has eight cartridges, each cartridge has 40 cards (and how many were there going to St. Ives, I wonder?).


The first six cartridges in each board are 2-inch alphanumeric displays, followed by two larger cartridges to display a 24-hour clock. Inevitably, just in the ordinary course of their use—to say nothing of the subsequent closure, abandonment, and decay of Mirabel—at least a few flaps would have gone missing. We had to get an overview to make sure we had a full set. Earlier this summer, I flipped through what should have been a total of six hundred and forty flaps, so we could make sure that we had a complete set. Incredibly, we’re only missing two.

I wrote earlier about our makeshift replacement flaps in this post, laid out in Adobe Illustrator and sliced from the matte black plastic file folders Matt had found in the Loyola Campus bookstore by Mark’s laser cutter. Next, we needed to get the letters printed onto the black plastic. In an early experiment, I wondered if we might be able to paint the letters on with a brush. It seemed like the best choice to start, given that we only needed two flaps. I marked off the bottom half of the test B with painter’s tape and gave it a go. However, when I carefully tweezed off the tape after the paint was dry, the results were less than inspiring. The edge was a bit ragged from paint seeping under the tape or being pulled off in the removal process, and the brush marks bunched and stripped the paint in varying ways across the surface. So, we needed a different option. MIT’s The Beach Lab, in an effort to make their split-flap display relatively inexpensive, opted for cut vinyl letters. You can learn more about that project here. But I was so taken by the crisp edge of the screen-printed letters of the originals, and wondered if the vinyl letters might stick out sorely in a cascade of printed ones. It looks like others have done this method also—of cutting the flaps first and then individually screen-printing—like this dance company in preparing a board for a performance about travel.

My pal Justin Gordon is one of the three founding members of the excellent Montreal-based printmaking collective and studio Atelier Lost Cause, along with Concordia fine arts students Gabrielle Mulholland and Hillary Barnes. I asked him if he could help us out with printing, and he said he could try. I’d traced both sides of our missing letters (top of an E/bottom of an F and top of a Z/dash) at the lab and taken them home with me. In order to screen print, you need the parts you want the colour to go in jet black, and the other parts white. I took the original layout of the split-flap I’d made in Adobe Illustrator to use for the laser cutting:Black and white outline of split-flap…and repurposed it for our four half-letters. I carefully measured the tracings and laid out the letters in Illustrator, filled them with black, and printed them out on ordinary paper (with back-ups—in case one of them didn’t work out).[6]

Overvew of four black-and-white letters with blue split-flap outline laid out in a grid. The top of an E, bottom of an F, top of a Z, and a dash.Justin laid all four letters out with oil on one screen, exposed it, and then we were ready to go. We laid down a test onto acetate so we could see where the print would land, lined up each black flap behind the acetate, and printed the letters. They were a bit sticky when they came out, and so we tried to dry them under a heat dryer, which resulted in melted plastic. A brief stint under the dryer, and then some time by an open window, and they were ready to print the other side. Here they are—crisp, clean, and smooth, and although the gloss of the letters isn’t exact, it’s a pretty good match.

[1] R. Port, “ICON, INDEX and SYMBOL (Short Version),” http://www.cs.indiana.edu/~port/teach/103/sign.symbol.short.html.

[2] Mac Daniel, “Nostalgia for noise at South Station,” Boston Globe, 6 April 2006, https://www.ble-t.org/pr/news/pf_headline.asp?id=15901.

[3] http://www.iridetheharlemline.com/2010/05/14/fridays-from-the-historical-archives-solari-departure-boards-photos-history/

[4] http://unknowndomain.co.uk/category/design/split-flap-display/page/6/

[5] http://www.railforums.co.uk/showthread.php?p=2255362

[6] I should have had both a copy with the outline of the flap for a guideline and one without for the printing, but I didn’t print the latter! This meant that Justin and I had to cut carefully around each letter, lest the outline of the flap be printed in white onto the edge itself.