Blacksmiths of ancient times never had the microscopic or technical tools to analyze the micro-structure of metals. All they could do is ensure quality only at the physical level. It is no secret now, that Indians used many more types of Irons than what modern metallurgists of today. Same was the case of most other metals.
Ancient texts like Rasaratna Samuchaya, Chanakya’s Arthashashtra and Rasa Shashtra describe the quality of pure molten metal as-
- No sparks- similar to how the visual purity of oil is tested. Sparks mean that the oil contain water and other impurities.
- No noise- noise in flowing metals is a result of solid or denser impurities present in the molten metals.
- No scum- scums resulted as a part of reduction of impurities in metals.
- Looks like gold- shows the aesthetics of ancient India.
With these simple yet effective metrics, blacksmiths had established themselves as great craftsmen. Modern engineers must learn to depend on intuition and knowledge than automating any challenge they face in the process of making the world a better place to live. Empirical knowledge has its own glory and must be used whenever possible. It has proven to be much more valuable than theoretic or academic knowledge in the long run.