How to mantain flat surfaces in Zbrush when polishing edges?

THRevY

Hello!

I have little experience in Zbrush and I've been attempting to learn about stylized sculpting for the past few days. I have found an interesting article belonging to Fanny Vergne in the Vertex book #2  related to sculpting stylized slabs of rocks. The end result of her sculpt is this: 

The rocky detail on these slabs comes, at least from what I understand, from alphas that she sculpts on separate cubes. The process for creating said alphas is something like this: 

1. Create a sharp mask for part of the cube

2. Move it backwards and sideways in order to give it that look of layered stone:

3. Now flatten that newly created edge and give it more sharp angles using a flatten or trim brush: 

This step is where my problem occurs and the reason why I hate sculpting rocks. As you can see, attempting to use the Trim smooth border on the new edge has the expected result, however it cuts into the initial plane (the one that was masked and moved) giving it a small bevel effect that will appear in the grabdoc of the alpha. My initial thought was to just keep the mask on while flattening this edge, however after moving the plane out and back, a dynamesh is pretty much mandatory to get rid of the stretched geometry. I didn't think this to be a problem at first, as my first instinct was that I'd just save the mask, re-dynamesh and the load the mask back. However, it appears that Zbrush cannot save masks of objects without UV Unwraps, which makes the prospect of exporting the object to another software in order to do the Unwrap, then back to Zbrush, quite unappealing. I have tried using various brushes (Trim smooth border, trim dynamic, Flatten, Orb Flatten Edge, hPolish and PlanarFlatten) however to no avail. Reducing the brush size does help in making the bevel a lot smaller, however unless I go in with a draw size of 1 it seems like the problem is ever present. Finally here's an image of the problem from above which showcases how visible it is from above: 

Here's a picture of Fanny's final sculpt before grabbing the Alpha. As you can  see her surfaces look just fine in places where planes meet, and she seems to have no weird bevels.

I imagine this problem is quite a simple one, so I'd like to apologize for asking about it in the first place, however this has been the bane of my existence as far as sculpting rock details for a long time now, and I've finally managed to muster up the courage and ask about it. Is it something that has a solution, or is it one of those things that you'll have to try and minimize as much as possible and live with?

Thank you!

gnoop

I am using Substance Designer currently for such things   but before I recall I used polygroups in Zbrush   "groups by Normals" most probably , then made not flat parts only visible and select them , then switched back to complette view and inverted the selection .

"Mask by feature"  also should help 

BagelHero

Brush settings also have settings for "automasking", which might help prevent this on especially sharp angles.

icegodofhungary

Yeah it's a combination of using auto masking under the brush settings. You also have to alternate between sub and add. Use the hotkey, alt, while sculpting. The trim brushes are sort like planar brushes. When you hold alt, start your stroke on the flat surface you want then drag to the area you want to fill in. It'll smooth out those little dents and add some height to your curve. Wax on, wax off until it looks right. Also try playing with the focal shift as that can alter how your brush handles itself around edges.