Drop Shadow Workshop
Even if it could be achieved, perfect transparency would be a dangerous mistake.
Windows and Mirrors, page 53
Firing up Photoshop and playing with typography, color, textures, gradients, drop shadows etc. it’s easy to generate some nice looking results fairly quickly. It’s also pretty gratifying to have what looks like a pretty and cohesive design to show someone else after a few hours of work. But aren’t we missing something here?
When Software drives Design, Ian Wall in his new blog humane machine.
Weder Veteranen noch Jungexperten brauchen hüpfende Icons beim Programmstart oder schattierte Fensterumrahmungen. Eigentlich sind ihnen Mäuse schon schwer verdächtig.
Marcus Hammerschmitt in seinem Essay Lob der Härte, Telepolis vom 21.03.2008
This pseudo-3D look results in a strong figure/ground effect—it attracts the viewer’s eye to the content. Fancy explanations aside, it just looks good.
Jenifer Tidwell im Kapitel “Deep Background” von “Designing Interfaces: Patterns for Effective Interaction Design”
Alles über das Wahrnehmung von Figure und Ground bei Wikipedia.

Dragan Espenschied in Contemporary Home Computing: The home computer presents itself through several interfaces, some in software, some in hardware. While it is mostly assumed that these interfaces’ goals are to expose the computing capabilities of the system to its user, obviously interfaces are at the same time responsible for transporting the image of the machine.

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Windows User Experience Interaction Guidelines, chapter Aesthetics, Icons, Shadows
Use shadows to lift objects visually from the background, and to make 3D objects appear grounded, rather than awkwardly floating in space.
Windows User Experience Interaction Guidelines, chapter Aesthetics, Icons, Shadows
Hypermediacy = style of visual representation whose goal is to remind the viewer of the medium.
Bolter and Grusin, Remediation, page 272
Immediacy = the symbol is simply perceived to be a window to the real.
Jennifer Stimson and Rich Rice, in the Glossary to their Review to Remediation by Jay Bolter and Richard Grusin.
Computer sind Modellierungssysteme. Sie sind darin sogar so gut, dass man leicht vergisst, dass die Welten, die sie schaffen, überhaupt keine Welten, sondern eben Modelle sind.
Douglas Rushkoff in Von Computern und Modellen, in Telepolis vom 7. August.2000