Why are the Bardi Chapel and Peruzzi Chapel frescoes difficult to study?

The frescoes in the Bardi Chapel and Peruzzi Chapel are difficult to study primarily because they were whitewashed for centuries and were not recovered until the mid-19th century.1

During the process of removing the whitewash, the frescoes sustained significant damage and subsequently underwent heavy restoration, which complicates the assessment of the original work. While mid-20th-century cleaning and re-restoration helped clarify their condition, the two chapels present different challenges:1

• Bardi Chapel: This chapel retains a few splendid figures painted in the true fresco technique.1
• Peruzzi Chapel: The figures here are now largely "ghosts" because they were executed using a different, less durable technique.1

These factors, combined with the historical layers of restoration, make it difficult to determine the exact dates of the cycles or to fully appreciate the original artistic intent compared to Giotto’s better-preserved work in the Arena Chapel.1