Taking Inventory

Invisiclues and a Call For Assistance

by Jason Scott on Dec.19, 2008, under production

Back in the beginnings of Infocom, part of the issues with having games based on puzzles were that some people would run into difficulties with those puzzles. As a result, they’d mail questions to Infocom for help. Hints, if you wish, that would help them move on to the next puzzles. Lacking anything like an easily-accessible website to get information, people would rely on these questions and answers via mail. And there were a lot of them. Mike Dornbrook at Infocom was tasked with answering a lot of these questions in the beginning of the company’s history (others helped as well) and eventually decided it would be a much smarter idea to create a pre-packaged collection of questions and answers for the games, which could then be sold as products, along with maps and t-shirts and anything else Infocom/Zork related.

A problem presented itself, though: people would only want a slight hint, a nudge in the right direction.  They didn’t want to be handed the whole answer and they certainly didn’t want a pre-printed list of all the answers right there either tempting or distracting them. Some research and thought went into this problem.

The solution that Infocom came up with were Invisiclues, which were booklets printed in invisible ink. You could see questions but you couldn’t see the answers. To see the answers, there was a special pen that came with the booklet, and as you needed help, you would rub the pen in a box and a hint would appear. There were a few boxes under each question, and from that you could slowly work up from a slight nudge to being handed the answer outright.

From the excellent infocom.elsewhere.org site, here’s an example of how this looked. (Don’t worry, it’s a page that has a meaningless example and no actual hints):

If you’re wondering about what would happen if you read all the questions and got ideas from them, Infocom thought that through too - a portion of the questions would be answers to problems not in the game, and would ridicule you for trying to cheat.  There was always, throughout the construction of these, an attempt to balance the need to know with the desire to come up with the final solution on your own, which was (after all) the whole point of playing these games.

The process of these Invisiclues is interesting. At the time this was utilized (the early 1980s) the term for them was “latent image printing”, and referred to images that were printed but required additional chemicals or processes to be found. In this case, the chemicals in the pen (which had a yellowish tint) would activate the chemicals in the printed text and cause that text to become visible. It is all explained not-very-clearly in this patent, in case you want to whip up a batch for yourself.

Speaking of which….

One of the concerns with my documentary is that it reveals the solutions to games in the course of interviews. I definitely don’t want people watching this film to be exposed to solutions of games they’ve just gotten excited about while watching my documentary. How lame would that be? So I’ve been considering ways to get around this problem.

One possibility, which I may do, is a selection from the menu on a DVD so there’s a spoiler and non-spoiler version of the movie. But the other… is invisiclues!

Besides allowing people the fun of what Invisiclues used to be like, they would serve a purpose, allowing people to unearth some hints about what people were talking about without dropping the total answer.. unless they wanted to hear it. It just strikes me as a fun idea.

The problem, though, is I have had an enormously hard time finding anyone who does it. If you have any idea, please write to me or comment below. Bear in mind, I spent a lot of time on this a while back, so here is what I know:

  • The place that probably makes the most of these types of book/pen combinations is Lee Publications. They have a wide range of books and even license very up to date properties to make books out of them. I can find absolutely no evidence that they would do an outside contract for someone to print, say, 5000 of these booklets. Maybe you can find a way?
  • With access to internal Infocom documents, I believe I have found the name of the company that did the original printing back in the 1980s. It seems to have been A.B. Dick company that made the “A.B. Dick Latent Image Pens”. Communication happens between them and American Printers and Lithographers over whether the pens are poisionous (they weren’t). American might have made the actual books themselves using A.B. Dick products. Both these companies were in Chicago. It’s been a bunch of years since then and I can find no evidence that either of these companies do this anymore.
  • It appears that several governments (NY and Federal) have tried to acquire these pens and paper for testing. Here’s a particularly dull example of that request. I find no indication they ever got them.
  • Possibly, just possibly, what used to be “latent image” printing is now under the header of “security printing”.

So I am not so much at a dead end but in a situation where I haven’t had time to track stuff down further. My suspicion is a lot of the really complicated jobs have moved to China, but that in fact may mean I just have to find the right US company that deals with China. Would you like to help?

Find out how I can do this, and you’ll get a credit in the movie.

Update: Dennis Jerz has put me in contact with Lee Publications and things looks like a deal might be worked out. Thanks a ton, Dennis!

7 comments for this entry:
  1. Daniel Auger

    True invisiclues would be cool, but if technical availability becomes a showstopper you could always go the filter/viewer route like the clues that shipped with Seastalker.

    That being said, I think some form of on-screen or alternate audio track clues/spoilers would be a good backup strategy. Think of it… The interviewee is about to reveal the fate of a certain sidekick, but the audio comes out akin to Charlie Brown’s teacher’s voice. However, the true reveal could be heard on an alternate audio track. This way you only have one visual cut of each scene.

  2. JayH

    A similar, but alternate, approach might be to use ink that’s only revealed under ultraviolet light, and ship some sort of small ultraviolet light source with the DVD. That may sound ridiculous, but currently there’s a toy mockup of the “sonic screwdriver” from /Doctor Who/ that includes both a “UV ink pen” and a “UV reveal light,” and it sells for only $17. (Check thinkgeek.com for details.)

  3. Jason Scott

    That is an excellent, excellent suggestion and one I may fall back on. One of the situations I didn’t quite know about the Invisiclues is they would fade after six months. That could be a problem right there, and worth going with the UV inks for.

  4. Jim Leonard

    Invisiclues would only fade after six months AFTER they had been revealed with the pen. Not sure if that’s what you meant.

    I will tap the software collecting community to see if they have any ideas.

  5. Martin T.

    Another option could be what some other game companies did with their clue books. I think Sierra did it first. Anyway you would have a book with the questions and the answers were under the question, but in blue ink with red ink covering the answers, then you used a transparent piece of red film to filter out the red ink and just the blue ink showed up revealing the answer. This site has a lot of scans of sierra’s old hint books and shows you what I mean.

  6. Drew

    I like Daniel’s idea best. The same effect could be achieved by putting a small alert bar at the bottom of the screen when a spoiler is coming up, so the viewer can mute their screen, or have the speakers words drowned out by the sound of the clicking keys of an Apple II (my first Infocom computer). Invisiclues were neat, but I want to see the documentary!! Why make it any more complicated than it has to be? Can’t wait…

  7. Daniel Auger

    JayH, that’s a great idea. Of course the obvious extension on that idea would be to have the light source look like a small lamp.

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