The Soroban Abacus Addition Method Explained

By now you know I've been an abacus aficionado for most of my adult life. Yet, despite the oddball nature of bead-frame calculators in the 21st century, I've met a number of people over the years who were actually interested enough in learning basic abacus addition to make an honest effort. Invariably, many of these adult learners would struggle with the concepts, never gain proficiency and eventually lose interest.

I was one of those adult learners who also struggled with some of the concepts, until I met a school teacher in Socorro, NM, a Taiwanese native and abacus user since her formative years, who showed me a few key concepts that made the Japanese soroban style of abacus much easier to use. In so doing I also noticed that the concept I struggled with was one she took for granted, having learned the soroban in her formative years, when the cerebral cortex is much more malleable. I soon realized that part of the problem was the nature of adult learners such as I.

My interest in the abacus waxes and wanes over the years, interspersed as it is with many other passions. Recently I've come to reconsider the problem of adult learners of the abacus, since I currently have an exhibit of my abacus collection on display at a local public library, and have been working to simplify the teaching of addition on the Japanese-style soroban.

The problem presented by the abacus is you have a limited number of beads available to represent numbers, thus when adding numbers together you frequently run out of beads, necessitating roundabout methods of completing the problem. I realized the seasoned abacus operator intuitively recognizes these various situations, on-the-fly, and immediately responds with the appropriate technique almost subconsciously, through rote training. What I immediately set about doing was documenting those various instances when alternative techniques are required to complete a calculation, with the goal of systematizing a formal methodology for approaching any addition problem.

Naturally charts and graphs would be employed, as I can imagine Arlo Guthrie explaining in his classic piece Alice's Restaurant Massacree: "...twenty-seven 8-by-10 color glossy pictures with circles and arrows and a paragraph on the back of each one explaining what each one was, to be used as evidence against us..." So be forewarned about the color glossy pictures ahead!

As I said, I've been using the abacus for years, with proficiency sufficient for basic addition, and thus I had to slowly unravel my thinking process of how I approach these problem situations. I started by mapping all of the possible addition problems and color-coding them with their requisite solution technique.

Figure One:

Addition problems on the soroban require four general categories of response. The first category, where the cells in the above chart are white, are direct-entry problems where no special technique is needed. Simply enter the starting number (indicated by numbers along the left column of the chart) and then enter the addend (indicated by numbers along the top of the chart) and the answer presents itself on the soroban.

Here, these direct-entry problems have been isolated from the rest of the cells:

Figure Two:

The second category of problem response are when adding numbers together that are both less than five, but there aren't enough beads on that rod to complete the problem. These are indicated by the cells highlighted in yellow, and marked with a "5" in Figure One. These cells are isolated in Figure Three, below. The solution of these problems require the employment of what are termed "fives complements."

Figure Three:

The use of complementary numbers is a technique designed to get around the problem of running out of beads to complete a calculation. Instead of adding the number, we subtract its complement and add the next higher bead. Consider the following table in Figure Four:

Figure Four:

The top row lists the digits 1 through 9, and the following two rows list the tens complements and fives complements of each number, respectively. The five complement of a number is a number that, when added to the original number, equals five. Similarly, the ten complement of a number is a number that, when added to the original number, equals ten. It is a requirement that the abacus operator know by heart both the fives and tens complements.

So, in this second category of problem the solution is found by adding a five bead to the rod and subtracting the fives complement of the number, in one swift downward motion of the index finger.

The third category of problem response are those whose solution is found by employing a tens complement operation, as indicated by the green cells in Figure One. With these problems, the tens complement of the addend are subtracted from the rod, then a single ("ten") bead is added on the next rod to its left. These problems have been isolated in the chart in Figure Five, below:

Figure Five:

There is a fourth category of response, indicated by the rose colored cells in Figure One, and isolated in Figure Six, below. These kinds of problems were the ones that I stumbled to understand, as they are ostensibly tens complements problems but require a fives complement operation to also be performed; what I call "nested" or "combined" complements problems.

Figure Six:

The shortcut method my abacus teacher taught me for solving these kinds of problems was to "push up" the number, then add the single ("ten") bead on the rod to the immediate left (instead of thinking of it as a fives complement problem nested within a tens complement problem).

In addition to categorizing the soroban abacus operations into four categories of response, I had to decipher in what order I tend to solve them in my mind; since I often solve the simpler problems automatically, with little conscious thought. In so doing I devised a checklist, in the form of three questions I use to interrogate a problem, resulting in the four possible response methods.

Figure Seven:

By following this checklist in the order suggested, the simplest solutions are arrived at first, followed by solution methods of increased complexity. I've found that following this sequence of questions always leads to a solution every time, but there are two additional complexities to unravel before we can call this bulletproof.

The last two solution methods involve tens complement operations, where a single ("ten") bead is added on the next rod to its left. However, there are two situations where that single ten bead cannot be entered.

Figure Eight:

As you can see from Figure Eight, above, if the rod to the immediate left of our problem is either a four or a nine, there will be insufficient beads available to complete a tens complement operation. In the case of a four, all the beads on that rod are lowered, while in the case of a nine, that rod is cleared and the single bead is added to the next rod to its left.

This is essentially all that one needs to know in order to master addition on the soroban. However, there are a few things I've left out, assuming you already knew them. The first is how numbers are entered. The abacus is "cleared" when the top and bottom beads are pushed away from the dividing bar. Numbers are entered when they are pushed toward the dividing bar. The four beads below the bar are each worth one point, while the single bead above the bar is worth five points.

Secondly, numbers are entered on various rods in place-value fashion, similar to how numbers are written on paper. For addition, multidigit numbers are summed from left to right instead of the more usual right to left. When adding multidigit numbers, each digit is treated as a separate single-digit problem, using the rules outlined above.

Finally, proficiency is only gained through constant practice. One easy practice method is summing the number sequence 123,456,789 ten times. In the process, every possible combination of addition problem will be encountered. You can easily tell if you've arrived at the correct answer because it should be: 1,234,567,890. This lengthy number should be compatible with any soroban having at least ten rods.

You can also use your grocery store and shopping receipts as another kind of practice problem. Add up the prices listed on your receipts and they should match the store's subtotal. This is a good way to bring some fun into the drudgery of shopping, as you look forward to adding up the receipt totals afterwards.

I've presented these techniques in a comprehensive video, embedded at the top of this article. My intent is, by following this method, addition on the soroban can be mastered by the average adult learner with but rote practice to gain proficiency and speed. I hope you will consider becoming an abacus practitioner.

Post-Script: I'm frequently asked for links where people can buy a soroban-style abacus at a reasonable price. Keeping in mind that artisanally-crafted Japanese soroban are works of art and their construction methods an official national treasure, I've found some inexpensive Chinese-made versions with beads sufficiently large for the adult westerner. Here is one such example: www.shorturl.at/tvwM8

Abacus Exhibit in Rio Rancho, NM

Japanese 1:5 Soroban with kanji characters on the dividing bar representing denominations of yen.



Central Asian Schotty, 10-bead abacus



10-Bead school abacus of the kind Napoleon brought back to France from the 19th-century Russian campaign.



Here are the presentation foils included in the exhibit:






The following pages illustrate examples of abacus addition. First is how numbers are represented on the 1:4 soroban:



Next are two simple addition problems, the first one direct addition, the second using fives complements. But first I should explain the concept of "complements."

Since there are a limited number of beads on each rod, there are occasions when you can't directly add a quantity of beads. For numbers under 5, these problems are known as "fives complements." A five complement is a number that, when added to the original number, equals five. For example, the fives complements of 1,2,3 and 4 are: 4,3,2 and 1, respectively.

There are also tens complements of numbers: a number which, when added to the original number, equals ten. The tens complements of 1,2,3,4,5,6,7,8 and 9 are: 9,8,7,6,5,4,3,2 and 1, respectively.

The way that fives complements are used in addition is, instead of directly adding the number (which you can't, because there aren't enough beads left on the rod), you subtract the fives complement of the number and add a five bead from above the bar.

The way that tens complements are used in addition is, instead of directly adding the number (which you can't, because there aren't enough beads left on the rod), you subtract the tens complement of the number and add a single bead on the next rod to the left.



Next is a problem involving both fives and tens complements. These problems happen when you have to do a tens complement operation, but there aren't enough beads on the rod to subtract the tens complement. The shortcut method my Taiwanese abacus teacher taught was to "push the number up," as illustrated in the next foil, where in order to add 7 to 6, you "push the 7 up":



The photo below shows the classic book on Japanese soroban, by Takashi Kojima; that I first acquired in the early 1970s when I began my abacus journey. The photo is also accompanied by a contemporary Chinese-made teacher's abacus, designed so the beads stay put when hung vertically for the classroom:



A Brief Primer on Soroban Addition:

Performing addition and subtraction (the inverse of addition) efficiently on the soroban means quickly determining which kind of operation you need to perform. Though I'm not a master soroban operator, I can work my way around the beads well enough for my purposes, enough to know that I often can enter each number without consciously thinking how I did it, through rote practice. But I've since analyzed my methods, and have determined the following procedure for beginners to follow for addition on the beads. This procedure is based on Kojima's teachings, but expressed in logical steps for the western adult-brained learner.

Firstly, you do need to know the fives and tens complements.

Next are a series of questions you need to ask, in the order listed, when confronted with a single-digit addition problem:

A) Can the number be directly added? If yes: add the number, problem done. If no, go to step B.
(Examples of this kind of problem: 1 + 3 and 2 + 7)

B) Are both numbers less than five? If yes, subtract the five complement of the number and add a five bead (this is done with one swift downward move of the index finger), problem done. If no, go to step C.
(Examples of this kind of problem: 4 + 3 and 3 + 2)

C) Can the tens complement be directly subtracted? If yes, subtract the tens complement and add a bead on the next rod to the left, problem done. If no, go to step D.
(Examples of this kind of problem: 3 + 8 and 9 + 6)

D) Push the number up, then add a bead on the next rod to the left.
(Examples of this kind of problem: 5 + 9 and 7 + 6)

There is one more complication. Sometimes, when dealing with multi-digit numbers, when doing a tens complement problem and you need to add the single bead on the next rod to the left, if that rod already holds a value of either 4 or 9, you can't directly add that single bead. If the rod has a 4, you need to swipe down the five bead and all four ones beads (essentially doing a fives complement operation in order to add the single bead). If the rod has a value of 9, you have to clear the nine out and add the single bead to the next rod to its left.

I should also mention that when adding multi-digit numbers, you do so from left to right, like the order in which you would write or speak them. This is more efficient than the right-to-left paper method we were taught in school.

I know that for the rank beginner this all sounds complicated. But what I've described thus far is all you need to know to do addition problems involving numbers of any length. You do them one digit at a time, from left to right, using the rules I've described above.

Know also that I will be touching on this method in more depth in an upcoming video on my YouTube channel.

Royal Mercury Platen Replacement

Removing and installing the platen was easier than expected - once I was able to loosen the left platen knob via a set of rubber strap wrenches, that is! I have Ted Munk to thank for sending me a page out of the service manual where it illustrates how to remove the platen:



I've yet to do any upgrades to the sound insulation inside the body panels, something that Ted has shown us how to do with his Brother project machine, but it should make this machine even quieter in use.

As for which ultra-portable in my collection is my favorite, perhaps that'll be the subject of another video. I still need to do more typing on this machine, and it also needs a darker ribbon, so I need to get an order placed (perhaps I'll get a bulk roll from Baco Ribbon Supply!). The favorite ultra-portable competition in my collection is between the Groma Kolibri, the Olympia Splendid 33 and this Mercury.

Here's Episode 300 of the Typewriter Video Series, about this project:

Tinkering With Old Cameras

Joe cleaning Zorki 1 parts



I was once a VCR and camcorder technician, back in the 1980s, when I was younger, had better eyesight and steadier hands. Even so, it was challenging, especially camcorders with their innards crammed with compact circuit boards connected together with fragile ribbon cables, and their miniature transport mechanisms that were a marvel of precision miniaturization. Electronic problems were approached using structured problem solving -- troubleshooting -- involving voltage and waveform measurements, assisted, if you were lucky, with service literature from the manufacturer.

But before these marvels of electronic and mechanical miniaturization there were all-mechanical cameras. Oscar Barnack, working for Leitz optics, around the WW1 timeframe invented the first practical rollfilm camera using 35mm motion picture film, which eventually became what we know as the Leica rangefinder. A dense, compact metal chassis crammed with precision machined parts and featuring rangefinder focusing mechanically coupled to jewel-like miniature lenses, Leica rangefinder cameras have remained even today the pinnacle of mechanical camera engineering. But back in the 1930s Soviet manufacturers began copying the early Leica screw-mount (so called "Barnack") rangefinder cameras, with sometimes dubious engineering and build-quality.



I've been using one of these, the Zorki 4, made in 1971, with its diminutive but elegant Jupiter 8 lens, since the 1980s. The camera has been remarkably reliable, considering I used to leave it in the glove box of my car, winter and summer; I've often wondered if its internals weren't lubricated with whale oil, because it never seems to have been bothered by the cold, despite its all-mechanical operation.

A few weeks ago my friend Ethan Moses began educating himself on Russian rangefinder cameras, by buying a handful of these old cameras from online auction sites. In the intervening time since they've arrived on his doorstep, he's learned to tear them down, service them and put them back together, mostly in better shape than when he started, with the exception of one or two early on that served as training aids. These all are, in some form or another, direct descendants (or knock-off clones) of Oscar Barnack's Leica, albeit with mostly inferior mechanicals. The Fed models (named after Felix E. Dzerzhinsky, head of the Soviet secret police) were the worst of the lot in terms of design and build quality, while the Zorki models were noticeably better. My camera, the Zorki 4, was probably the height of Soviet rangefinder camera technology, in terms of build-quality and features, but it is the little Zorki 1 that surprised both Ethan and I.

The Zorki 1 lacks the slow-speed timer mechanism of the later Zorki 4, meaning the slowest timed shutter speed is 1/25 sec. It also has separate rangefinder and viewfinder windows, meaning you first focus on your subject in the rangefinder window (by turning the lens focus ring and aligning the double images where you want the image to be most sharply focused), then move your eye to the viewfinder to frame your shot. The Zorki 1 also lacks the nifty adjustable eyepiece diopter of the Zorki 4, a boon to eyeglass wearers. But where the Zorki 1 lacks in features it makes up for in diminutive form factor. Compared next to each other, the Zorki 1 top plate barely pokes above the upper trim line of the much taller Zorki 4.

Ethan and Zorki 1 in hand

Though metallically and mechanically dense in heft, the Zorki 1 fits in the hand very comfortably and is easy to carry around, especially with a collapsible screw-mount lens attached. It also lacks strap lugs, meaning you either have to use the original leather case (which are rather rare), or attach a 1/4-20 strap lug fitting to the tripod socket. I think it feels best in hand sans strap altogether. Also lacking a built-in light meter, the best way to use these cameras is use a light meter app on your phone, take a reading, transfer the settings to the camera and then just go shooting and not worry about further metering unless the light significantly changes, relying instead on the exposure tolerance of film. The ultimate in simplicity.

I often hang out at Ethan's on Tuesdays, and these last few weeks I've watch him tear these cameras apart, describing to me each part's function, watching him learn the ropes as he becomes more adept at servicing them. Sometime after Ethan gained confidence in servicing Russian rangefinders he tried his hand at a Japanese-made Canon rangefinder.

In comparison to the more primitive Soviet cameras, the Canon seemed over-engineered in complexity, making it much more difficult to service. What makes this ironic is these Canon rangefinder cameras don't seem to garner the prices on the used market of the original German screw-mount Leicas, meaning there's little sense in buying one if it needs servicing, you're better off just getting a Leica instead.

Yet, despite the challenges, working on the Canon was a valuable education for both Ethan and I. Based on his past experience with the Soviet cameras, Ethan could identify each module of the Canon's mechanism, noting the similarities and differences in how specific functions were carried out.

The analogy that came to my mind as I observed Ethan tear down and rebuild these intricate mechanisms over the course of the last few weeks is that they serve as a form of mechanical logic: one linkage pawl gets held back by the slow-speed timer, preventing the second shutter curtain from releasing until the slow-speed clockwork winds down, then the second shutter curtain is released, ending the exposure. In a digital camera this logic would instead be performed by firmware in a silicon chip, but in these cameras the "programming" was strictly by means of an intricate interaction of mechanical parts.

Taking the Aardvark for a Walk

This is the Aardvark, a pinhole camera design I collaborated on with Ethan Moses, inspired by a camera sketch in a journal from years ago. Like many of my camera designs, it attempts to solve the problem of how to carry multiple large format paper or film negatives out in the field.

One such solution, which most photographers with any sense would use, is to carry sheet film holders. Which I have a number of. But that's not the point, is it?! No. The point is that I like to think up novel ways of solving these kinds of design problems.

Another solution I've explored over the years are falling plate cameras. But we won't discuss those today. Today we will talk about the Aardvark, a camera with an arm sleeve attached to the back, and a rear door that pivots open, inside the arm sleeve, to gain access to a paper/film storage compartment and a place to load the camera. Here's a picture of the camera, as it was being built, before the arm sleeve was attached.



The wide storage slot in the back uses a floating divider, just a piece of spare cardboard or plastic, to divide exposed from unexposed film or paper. You get to decide which way to use it; I prefer the unexposed sheets toward the front and the exposed sheets toward the back.

Just in front of the hinged compartment is the flange for loading the camera. It's a U-shaped flange that the paper or film is set into. Then, when the hinged door is closed (and clicks securely shut via rare earth magnets), the film or paper is securely clamped into place at the film plane, ready to expose. Closing the door also makes the rear of the camera light-tight, meaning it's safe to remove your arm from the sleeve, should you decided to do so. Or, you can keep your arm in the sleeve, if that gives you a greater sense of security, because some people had rough childhoods.

Here's a silly shot of your's truly with his arm in the sleeve, like a puppet. Puppet cam, heh, I like that!



The arm sleeve is made from two layers of blackout fabric, taped together with gaffers tape. No stitching, but thus far no problems with the tape coming loose.

Now that you know how deep that film/paper storage compartment is, it's easy to imagine how many sheets you could bring with you on a photo outing. Today, Ethan and I took a stroll in downtown ABQ with a dozen sheets loaded. Not a huge amount, but enough to test the camera in realworld conditions. As opposed to artifical world conditions.

The paper used was Freestyle Photo's Arista brand of grade 2 RC paper, which I pre-flashed ahead of time in my darkroom. The camera has an F/240 pinhole and I rate the paper at ISO 12. I was using the Pinhole Assist App on my iPhone as a light meter, and the recommended exposure times were rather accurate, as all twelve images had good exposures.

So how did the arm sleeve/paper storage slot system work out? I made the sleeve larger in size up toward where it mounts to the door flange, and that's good, because you need the room to maneuver the paper to and from the storage compartment. It could afford to be a bit roomier, but I made do.

One other problem I had early on was when returning the exposed paper to the rear half of the storage compartment, the paper already in there wanted to fall back toward the rear of the compartment, making it difficult to keep unexposed and exposed separated. I found the solution was to tilt the camera forward on the tripod head so it was pointing towards the ground, then the paper in the compartment would fall forward, making it easy to insert the exposed sheet into the back of the pack.

The camera has a very wide angle of view; the focal length is only around 35mm, so the images have some vignetting; but the relatively small focal ratio means the exposure times were conveniently short; some of them were only 5 seconds long, which is pretty short for paper negatives.

Once we finished, we processed them all in batches of 3 or 4 at a time in a large developer tray. I did the developing step while Ethan did the stop bath and fix. Tag-team processing like this is very efficient. Here are a few of the images we got today.


Ethan at Elm Park


Albuquerque Press Club


Ethan Downtown ABQ


Ethan on big chair at City Plaza, downtown ABQ


Ethan on Rt.66, downtown ABQ


Tract Home, NE ABQ

Type-Writing Versus Hoarding

I was asked by a viewer to post my notes for the recent video titled "Write or Hoard?" -- so here they are. Keep in mind that these are a first-draft work, complete with typos and corrections both typed and penciled in, originally not intended to be published. I did the video using this sheet (below) as a reference. Which was a bit odd, as I kept looking off-camera and referencing what I'd typed. In the future I need to learn to do this with more polish.



Parenthetically, I've started to really enjoy using a bichrome ribbon to make colored corrections and emphases. Especially with these 1.5 line spaced machines, like this Hermes 3000 The Elder. I'd really like to do this on my Splendid 33 but it doesn't have a bichrome setting. Does this mean I'm in the market for a Splendid 66 or 99 also? Not officially. Not if you asked my in front of my wife, for example. Only theoretically. Just for conversation's sake, of course.

But what I have done on the Splendid 33 is, in 1.5 line spacing, the same X-out corrections that are typed 1/2 line above the typo. And for emphasizing words and phrases a simple black ink underline seems to work fine.

Several weeks ago I started getting in this goofy mood where I'd type things conversationally, with my speaking voice (or the voice of some imaginary character) and purposefully underline words and phrases to gain a sense of the character's speaking mannerisms without going FULL CAPS, the way people emphasize certain words by raising their voice. This functions like a superset of phonetics, but operates at the whole sentence level. In "proper" writing you're not supposed to write this way, but I think it's a novel way to capture someone's speech mannerisms. After all, it is a constantly evolving language. ISN'T IT?

Diazo Paper Direct Positive Prints

It took me a while to get an acceptable pre-flash test strip. Part of it is you have to use a light source with sufficient UV light; then you have to expose the paper under consistent conditions (distance from light to paper) and exposure times for each section of the test strip. For my pre-flash testing I used a Viltrox LED light panel, that is adjustable for intensity and color temperature. I adjusted the output to 100% and the color temperature to 5600k, the most blue it would produce. My distance between light and paper was about 8 inches.



For this test the first section, at 3 minutes looked acceptable to me, so I used it for the remainder of my test exposures. Being as this is a direct positive process, the unexposed parts of the paper develop as deep blue, under the action of ammonia vapors. You can see the border of the test sheet, above, is dark blue, as it didn't get exposed to light during the test.

The diazo process is slow -- slower than mollases, slower than wet plate collodion even. It isn't meant for pictorial photography, which is why it presented an immediate challenge to me. Two plus hours exposure at F/5.6 is dang slow, and one of the main challenges to using this paper in larger format cameras, since fast aperture lenses get increasingly more expensive and rarer with larger formats -- the volume of glass in the lens increases as the cube of the format size, to maintain an equal focal ratio. For this test I used the F/5.6, 135mm Fujinon lens in my 4"x5" Intrepid field camera.



During these winter months only the middle of the day presents enough light to make this process practical; and even then, the exposure times are long enough to eat up much of that midday light. Here's a view of the Intrepid aimed at my backyard scene. To make this 2 hour 15 minute exposure I just pulled the dark slide and opened the lens, no timed shutter was necessary.



Because of the short opportunity to do test exposures, I decided to also use my 8"x10" sliding box camera, which had been sitting idle for months. It's equipped with a Fujinon Xerox process lens of 24cm focal length and a fixed F/4.5 aperture. The lens lacks a shutter and the aperture if fixed, but that's fine with this slow process.



I started the 8x10 camera exposure about 15 minutes after the 4x5, but later I realized that because the lens on the 8x10 is faster, the exposure should have been cut much shorter than the 2 hours 15 minutes. The resulting image was over-exposed and not worth posting, but lesson learned, it will be important to correlate a meter reading of the light with the necessary exposure time. Peter's tests show the paper needs about +18 stops exposure over an ISO 6 meter reading.



There are a number of things I need to work out before I can use this process more seriously and with greater consistency. They are, in no particular order:

Pre-Flashing: I feel it would be simpler to open up the dark slide and directly expose the paper to the sun (or shaded daylight, depending on the situation), immediately before starting the in-camera exposure. This would eliminate the need for a dedicated pre-flashing light source back home. This exposure time would need to be correlated to the intensity of both direct sunlight and shade, to offer both options.

Metering: I need to verify Peter's +18 stops over ISO 6 finding, and begin using a meter and calculator and/or reference chart in determining exposures more accurately. One of the main motivators is time: the process takes so long, you don't want to waste a 2 hour exposure on a botched calculation.

Reciprocity Failure: I don't know if this emulsion suffers from reciprocity failure under dim light, but it would need to be tested to verify.

Toning: The dyes in the resulting blue image will fade over time with exposure to direct sun, so it's important to keep them archived in light-resistant enclosures. But since silver gelatin photography has traditionally used various toning chemicals to not only alter the color of prints but enhance their longevity, it would be important to experiment with various toning compounds, especially selenium toner, as this has a positive effect in enhancing the durability of silver gelatin emulsions against oxidation and environmental chemical corrosion. Granted, these blue, iron-based emulsions aren't the same as silver, but there might be some possible solution here. There's also the possibility of, like with cyanotype prints, toning the prints to change their color, for instance with black tea or coffee. While these color-changing tones offer various aesthetic options, not all of them are healthy for the longevity of the paper, especially if they are acidic.

Dedicated Diazo Cameras: Given the length of time required to make a daylight exposure, you don't want to just leave an expensive camera and lens outside for hours unattended, and it would be inconvenient to have to babysit a camera for 2+ hours. Perhaps an inexpensive but fast lens could be found (like a single element meniscus lens from a surplus optical house) of the proper focal length and aperture, allowing cheap foamcore-board cameras be build for dedicated use with this process. Make several such cheap cameras, with the paper pre-loaded inside, no sheet film holders needed, and set them up in the daylight for several hours, then come back later to retrieve them (or lament the fact that these jerks around here will steal anything, even handmade foamcore cameras!)

This is a very inconvenient process, and the results are only marginal in quality. Which makes it perfect for the photographic experimenter! Yet it intrigues me with its possibilities. Stay tuned for more on this.

Here's a video about today's experiments: