Fig. 5
![Fig. 5](http://media.springernature.com/full/springer-static/image/art%3A10.1186%2Fs40494-019-0346-y/MediaObjects/40494_2019_346_Fig5_HTML.jpg)
OM photos and SEM–BSE images of the reddish purple glaze surface: a, b linear patterns resembling earthworm-walking patterns, i.e. the area with crystals corrosion only at the glaze surface; c, d the corrosion area, columnar pits and craters spreading to inner glaze (where white arrows pointing to), e, f secondary phases precipitated crystals in pits and craters (black arrow), pits without crystals (where white arrows pointing to)