An invention of Atrus which allowed him to emulate the properties of the ink and view other Ages by technological means.

One of the primary goals was to determine the status of Riven (which neither Atrus nor Catherine had seen for a long time) and ensure the status of Gehn, who had been trapped there. Unless he was sure that Gehn had no Linking Book to K'veer, Atrus would not risk linking there (and leaving a book behind).

It is known that Atrus had been working on the Crystal Viewer concept for several years and met many dead ends. He came close to success on Everdunes. Certain properties of the ink could be simulated with the right diffractive resonance of certain crystals, which could produce a visual link to one of the infinite Ages. That link was only visual, since without the Ink, the crystals do not bind onto a particular Age.[1]

The crystals' sympathetic harmonics were a problem, so he continued in Rime, an Age with naturally cold environments, since the low temperatures would dampen the sympathetic harmonics.[1] He then discovered that thin slices of geode (with a pure, protected, crystalline interior) below the crystals acted as more active suppressors to the sympathetic harmonics and also slightly amplified the clean frequency.[1]

The link, being visual, had an interesting advantage: it could be adjusted by changing the crystals, and display a vast number of distinct - though similar - Ages.[2]

Eventually Catherine was persuaded to come to Rime, with the hope to see Riven in the crystal viewer, and encouraged Atrus to uncover the combination, consuming herself with the set-up of the geodes and crystals. Atrus used his viewer to see Riven,[2] as well as Spire and Haven.[3]

As the viewer did not show much, he began considering how to improve, or even redesign, the mechanism in order to achieve a tighter image. During preliminary testing he found increasingly difficult to work in the cold; as such he sought a way to induce extreme temperatures artificially, so that he could install it in Tomahna. For this, he experimented with liquid gases, and found a workable pressure variable.[3]

He enlisted help from the Guild of Mechanists and Guild Master Andritus. Employing evaporator coils he was able to achieve a blurry image within the new viewer’s blank book. As a more powerful suppressor was needed to stabilize the image, he installed geodes inside the roof of his Tomahna observatory and focused them with an antenna, amplifying the clean frequency. Thus, he managed to see Rime, Spire, and Haven and even saw that Sirrus was making electrical constructions in Spire.[3]

However, curious bursts of interference destabilized the image. Atrus first assumed it to be a problem with the geodes, but then realized it was subsonic in origin, caused by wave fluctuations emitted by one or more Ages picked up by the roof antenna. Atrus used this as an opportunity to hear sounds from an Age.

By combining the resonances of five crystals together, a global pattern of emissions (a unique sound signature) could be discovered. Andritus assisted Atrus with a filtration panel that could make the antenna hone in on wave fluctuations and detect sounds. It was the first time Catherine heard the scary sounds of Haven and worried for Achenar. He also had an idea for an attachment that would change points of views.[3]