Question regarding macro-etch pattern

[tm0284]

This macro is of a HSLA steel. On the left 1/3 of this macro a smooth grey surface can be seen. On the right 2/3 the surface is patterned with with white, grey, and black. I've seen numerous macros where the entire surface looks either like the left, or the right, side of this photo. I haven't seen too many pictures like this one with both patterns.

I was just wondering why the right side of this photo looks so much "messier" than the left side of the photo. Is this pattern just a result of how the etchant dried? Or is there some other cause to it?

I've been curious about this for a while and hope someone can help me out.
Thanks

 

[metengr]

The application of the macroetch, dwell and surface cleanliness prior to the etch will influence the features you observed.

 

[tm0284]

Thanks metengr. I had always suspected it was due to uneven echant application because of poor grinding /surface preparation but wasn't sure.
While on this topic, do you have any reading recommendations or tips for interpreting the Mannesmann scale, particularly in cases where an image appears to be borderline?

 

[metengr]

https://www.researchgate.net/public...on_in_Continuously_Cast_Line_Pipe_Steel_Slabs