Were feathers added to Archaeopteryx fossils?

Dr Walt Brown says yes.  From the Center for Scientific Creationism:

Archaeopteryx means ancient (archae) wing (pteryx). But the story behind this alleged half-dinosaur, half-bird is much more interesting than its fancy, scientific-sounding name or the details of its bones. If Archaeopteryx were shown to be a fraud, the result would be devastating for the evolution theory.

Since the early 1980s, several prominent scientists have charged that the two Archaeopteryx fossils with clearly visible feathers (the Berlin and London specimens) are forgeries.1 Allegedly, thin layers of cement were spread on the mating surfaces (slab and counterslab) of two fossils of a chicken-size dinosaur, called Compsognathus (komp-SOG-na-thus). Bird feathers were then imprinted into the wet cement.

This apparently is from Brown's 2008 edition of In the Beginning; compelling evidence for creation and the flood (the link is to a different edition).

Things go wrong in the first paragraph.  If Archaeopteryx were shown to be a fraud, scientists would continue to use all the other feathered dinosaurs that have been found. Flying Dinosaurs has a long list of feathered dinosaurs.

From the Smithsonian:

In 2012, paleontologists found that a T. rex relative, Yutyrannus huali, had filamentous feathers. If a relative had feathers, why not the king of reptiles itself?
Until a specimen is found with preserved imprints of feathers, though, the jury is out.

Carl Zimmer has more:

Now Archaeopteryx is sinking back into the crowd of primitive birds and feathered dinosaurs. As Ed Yong has ably explained, a fresh wave of fossils are coming to light. They reinforce the argument that paleontologists have agreed on for a couple decades now: birds evolved from a lineage of dinosaurs called theropods. But it’s less clear now how exactlyArchaeopteryx fits into that evolution. It might still be closely related to the ancestors of living birds, or there might be non-flying theropods that were more closely related. Combine this with the recent discoveries of heavily feathered dinosaurs–feathered down to their feet, in fact–and the possibility emerges that dinosaurs evolved into flyers more than once. We look up in the sky today and see the results of only one of those transitions.

National Geographic goes even farther.

Over the past two decades, discoveries in China have produced at least five species of feathered dinosaurs. But they all belonged to the theropod group of "raptor" dinosaurs, ancestors of modern birds. (Related: "Dinosaur-Era Fossil Shows Birds' Feathers Evolved Before Flight.")

Now in a discovery reported by an international team in the journal Science, the new dinosaur species, Kulindadromeus zabaikalicus (KOO-lin-dah-DRO-mee-us ZAH-bike-kal-ik-kuss), suggests that feathers were all in the family. That's because the newly unearthed 4.5-foot-long (1.5 meter) two-legged runner was an "ornithischian" beaked dinosaur, belonging to a group ancestrally distinct from past theropod discoveries.

"Probably that means the common ancestor of all dinosaurs had feathers," says study lead author Pascal Godefroit of the Royal Belgian Institute of Natural Science in Brussels. "Feathers are not a characteristic [just] of birds but of all dinosaurs." (Related: "Dinosaur Feathers Changed With Age.")

So already Brown seems to be in trouble.  On to the second paragraph. "Several prominent scientists" seems to be light on actual paleontologists. Fred Hoyle and N. Chandra Wickramasingh are mentioned.  They are both mathematicians and astronomers but have no obvious background in the study of fossils.

At The War For Science, they note that no such cement has been found by other researchers.

Palaeontologists that examined the London Archaeopteryx arrived at a quite different conclusion - “Proof of authenticity is provided by exactly matching hairline cracks and dendrites on the feathered areas of the opposing slabs, which show the absence of the artificial cement layer into which modern feathers could have been pressed by a forger.”.

War For Science quotes (above) from this Science Mag article.

For more information, have a look at Kevin Padian's slides from the 2005 Dover Creationism trial. I used Chrome's highlighter extension to highlight some of the text near the slides which I feel carry all the relevant information.