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Before dawn, he withdrew the last probe from the vacuum tank, scraped the flecks of Aquadag into a bottle, and deposited it at the Rat House for Ruben.

Their carbon preparation was a paint-like graphite suspension known as Aquadag, which they smeared onto probes for insertion into the cyclotron tank to be bathed in the deuteron beam for days at a time.

Periodically Kamen would withdraw a probe and chip off the irradiated Aquadag, trying not to think about the exposure he might be absorbing.

The mixture with water is sold under the name of "aquadag," with oil as "oildag" and with grease as "gredag," for lubrication.