After glazing, the panel is relatively clean. However small amounts of putty or other residues musts be removed so that the panel is perfectly clean. Sometimes a few numbers remain of the pieces and need to be washed off. Cleaning, to be effective is done while the window is standing and receiving transmitted light. A final, final cleaning is done at the time of installation to remove any errant fingerprints, dust or other residues. Frequently, everyone in the studio pitches in on the cleaning, because it is so easy to miss small spots, especially on intricate windows.