Boyd’s Bible Dictionary:

An alloy of copper and zinc, not known to the Jews. The brass of Scripture was probably copper, or a copper alloy (Gen. 4:22; Deut. 8:9; Judg. 16:21; 2 Kings 25:7; 1 Sam. 17:5; Job 28:2; 1 Cor. 13:1).

Concise Bible Dictionary:

As “brass” is a compound, it is probable that copper is the metal often alluded to in scripture. See Deuteronomy 8:9. In some cases it may be “bronze,” as it is known that this was in use in ancient Egypt. The Hebrew word nechosheth is translated “copper” in Ezra 8:27, where it is said to be “precious as gold.” Brass is used as a symbol for righteousness according to the claims of God upon man, as in the brazen altar; the Lord as seen in the vision in the Revelation has feet like fine brass, “burning as in a furnace:” that is, righteous judgment according to responsibility (Rev. 1:15; Rev. 2:18).
Copper bracelet with two brass brands—1900s—US