The Dummy Mummy
The Mississippi Department of Archives received a few nice archaeological discoveries in the early 1920s, including several Native American artifacts and what appeared to be a "bonafide" Egyptian mummy. The mummy was tiny, prompting speculation that it could have been a kid. It remained on display until 1967, when Gentry Yeatman, a medical student, requested permission from the museum to study it for a research project. Yeatman found out the mummy was a fake when his request was approved.
Yeatman noticed the shredded newspaper shards stuck to the mummy's back as the first indication that things wasn't quite right. The student then used an x-ray machine to examine the object and discovered that it was made of papier-mache over a wooden frame that was kept together by nails and animal bones.
The two newspapers with print still legible on their pages are proof that the fake wasn't even done well. One of them was from a German-language publication, while the other was from the 1898 edition of the Milwaukee Daily Journal.