Unusual Etch on a Moro Blade

[Battara]

The only thing is that the original blades that survived with their original etch were not blue but brownish. In fact, Moros used this old formula:

1. cover the cleaned blade with citrus juice (like calamansee, a type of lime)

2. place in the hot sunlight

3. wait

4. wash off with water

The result was a grey to brownish color on the laminations of the blade. Sounds similar.