Hello @sboerner !
You have posted this in the ZBrush Core usage questions forums. Because ZBrush Core does not contain features related to texture creation or export, I will assume you are referencing the full version of ZBrush, and I will move your question to the appropriate forum.
Everything I’m about to go over can be found in the ZBrush Documentation:
http://docs.pixologic.com/getting-started/
I highly recommend reading the “getting started” documentation in its entirety, as well as for every feature you’d like to use.
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- Materials | ZBrush Docs
ZBrush has a finite number of material slots available. A custom material will overwrite one of the other materials ZBrush loads with. To save a copy of the active custom material, use Material> Save As. That custom material can then be loaded over top of any active material in ZBrush (Material> Load), and any polygons that have that material slot applied will now show the new custom material instead.
Please understand what information is saved with what kind of file in ZBrush. A Ztl will save the geometry of the active tool and not much else. To save any applied custom materials in the file itself, you would need to save as a ZPR.
http://docs.pixologic.com/getting-started/basic-concepts/saving-your-work/
EXAMPLE: For instance, if you have applied the default red wax material to areas on your mesh and save it as a ZTL, it will load with the Red Wax applied because the ZTL format does not save custom material info, but it does remember which slot is applied. The red wax is the default material that occupies that slot.
If you overwrite the red wax slot with a custom material, apply it to a tool and save it as a ZTL, the tool will still load with the red wax material applied, because it remembers the slot, and not the custom material info. But if you select the red wax from the material menu and select Material> Load, your custom material will overwrite the red wax in that session and appear everywhere on your model where the red wax was applied.
If you fill your mesh with a custom material and save it as a ZPR, it will remember all custom material information applied to a mesh anywhere in the scene.
- Keeping in mind the points above, simply load your custom material into the session, and with the M or MRGB channels active, use Color> Fill Mesh. This will fill any visible, unmasked polygons with that material as polypaint. Please be sure to understand how polypaint works:
http://docs.pixologic.com/user-guide/3d-modeling/painting-your-model/polypaint/
Polypaint is essentially vertex paint where color is applied directly to mesh itself. Detail capacity will depend on the resolution of the mesh. Note that polypaint is entirely separate from UVs or Textures. If rendering in ZBrush, polypaint may be sufficient for rendering with ZBrush’s extreme polycount potential. If you are looking to render in an external application, you will probably need to convert that polypaint to a texture and export it.
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- Dynamesh or Live Boolean can be used to fuse geometry together. After which, it would probably be a good idea to remesh your mesh into a multi-resolution form with clean, export-level base topology and multiple subdivision levels. Detail can be projected from a previous version of the mesh, onto the newly retopologized mesh, using one of the various methods for doing so.
If you are working with a process that will involve a lot of changes to the form and topology of the mesh, it is at this point it is recommended to create your UVs. UVs both affect the performance of the mesh at high polycounts, AND provide an opportunity for things to go wrong if applied to a mesh that will be undergoing heavy editing, so it is advisable to work without them until your topology is stable, and you are ready to create textures for export. Polypaint does not require UVs, and can be more easily transferred between different topologies, so it is better to rely on Polypaint while working rather than applied textures. That polypaint can be converted to a texture when your topology is stable and of higher quality.
Be sure to understand the difference between Material, Texture, and Polypaint. Materials in ZBrush refer to the surface qualities of a mesh when rendered. This is similar to shaders in other programs. Materials can sometimes be approximated between rendering engines, and there are exceptions–but generally speaking, each rendering engine does things its own way, and these arent going to transfer on a 1 to 1 basis from program to program. If you want to recreate the ZBrush Red Wax you can get pretty good approximations of it, but its not going to look exactly the same outside of ZBrush.
Textures are image maps containing color information. They will require UVs to display the color in the correct areas. Each program also has its own way of reckoning worldspace, which may require you to flip image coords along one or more axes to display correctly in your target program. Every program is different, and you will need understand your target program as well as ZBrush to get results.
Polypaint can be converted to a texture for export using the following process:
http://docs.pixologic.com/user-guide/3d-modeling/painting-your-model/texture-maps/
Good luck!