Authenticating unsigned bronze sculptures requires a combination of scientific techniques, historical research, and expert evaluation. Here are the most effective methods to determine authenticity:

1. Material Analysis: Advanced techniques like X-ray fluorescence (XRF) and metallurgical testing can reveal the alloy composition, confirming if it matches the expected period or artist's preferred materials.

2. Patina Examination: Genuine antique bronzes develop a natural patina over time. Experts assess its texture, color, and layering to distinguish between authentic aging and artificial treatments.

3. Stylistic Comparison: Comparing the sculpture’s style, motifs, and craftsmanship to known works by the suspected artist helps identify consistent techniques or discrepancies.

4. Provenance Research: Tracing ownership history, exhibition records, and archival documents can provide crucial clues about the sculpture’s origin and legitimacy.

5. Foundry Marks & Casting Techniques: Even unsigned pieces may bear subtle foundry marks or exhibit casting methods unique to specific eras or workshops.

6. Expert Consultation: Reputable appraisers or art historians specializing in bronze works can offer invaluable insights based on decades of experience.

For high-value pieces, combining multiple methods increases accuracy. Always work with certified professionals to avoid costly misattributions.