1)
What is "Mezukak"?
1.
'Rashi': It is very white. One can spread on the wall only something refined, be it gold or silver.
2)
Why does it say that the Kesef Mezukak was spread on the wall? They covered the walls with gold - "v'Es Kol ha'Bayis Tzipah Zahav" (Melachim I, 6:22)!
1.
Radak: "To spread" refers to the three Kikarim of Zahav.
2.
Radak (from Shir ha'Shirim Rabah 3:3): It was gold; it is called Kesef, for it was Machsif (embarrassed) all those who had [other] gold.
