If the glaze layer is relatively thin, it is enough just to apply some color to the surface, but if the glaze layer is thick then a bit of re-glazing is in order. Glazes from different dynasties are different in color, moreover, so you will show yourself up as an amateur if you use a Ming color on a piece from the Song Dynasty.
若是釉層較薄，只要「上色」即可，但若釉層很厚，則要先「補釉」，而歷朝的瓷器釉色各有不同特色，如果明明是宋瓷，卻給它戴了一張明瓷的臉，那就貽笑大方了。