http://revach.net/article.php?id=1898

Section: Parshas HaShavua   Category: Quick Vort
Parshas Vayakhel: Mirrors, Are They Good Guys Or Bad Guys?
 Rashi writes (38:8) that Moshe initially refused to accept the mirrors, which the women wanted to donate for the Mishkan. He found them disgusting because they were designed to incite a person's Yetzer HaRa. Until Hashem commanded him to accept them ,since the women had used them to arouse their exhausted husbands in Egypt, thereby enabling the conception of their children. Why didn't Moshe express similar reservations about accepting the Kumaz, (an acronym for Kan Makom Zimah) which Rashi explains (35:22) was a type of ornamentation placed opposite the private part of a woman's body?

The Meforshim offer a few answers. Some say that the purpose of the Kumaz was to stop someone else from being Mezaneh with this woman. It was a type of protection against the Mezaneh. Therefore Moshe was willing to take it as a donation. It was not a means for Znus, rather a protection against it.

Others answer; the copper mirrors were kept in their original state to make the Kiyar. Anyone who saw the Kiyar would know immediately where this copper was taken from. Therefore Moshe was hesitant to accept them. However, the Kumaz was just 1 of many golden ornaments which were donated by the women. They also donated bracelets, rings and nose rings. All these ornaments were melted down for the gold of the Mishkan. For this reason Moshe has no issues in accepting these pieces of jewelry.