The Brass
Scholars have said that seeing copper in a dream carries negative connotations related to behavior and morals. If one sees his thighs transform into copper, it indicates that his kin will be bold in disobedience. Additionally, seeing brass (a type of copper) being melted may point to quarrels over worldly matters, and it also signifies evil speech and slander.
Per Ibn Sirin's Muntakhab al-Kalam fi Tafsir al-Ahlam
Note: These are traditional scholarly interpretations (ijtihad) drawn from a specific classical source — not a binding religious ruling, fortune-telling, or a prediction of the future.