Making Veins in Blender

 I've made a few monsters that have needed veiny surfaces, from plant monsters to other things.  On those models, I've pulled out the sculpting tools and have made them by hand.  While I've been generally happy with the results, that process has been both labor-intensive and inflexible (meaning that it's difficult to change things around after they've been sculpted).  I'm working on another model that needs some veiny texturing and figured out a much better way to do it... so now I'm sharing what I've done!

First, I want to say that these screenshots are from the really early prototyping phase for this model, where I'm testing out techniques and trying to figure out what this thing's going to look like overall.  But, I was so happy with this vein technique, that I decided that I wanted to write about it... so here we are!

I like these veins for a few reasons.  Firstly, I think that they've got a good organic aesthetic, particularly at the intersections and how they taper off at the ends.  Next, they've got very stark lines, with the vein sharply defined from the surface that it's protruding from.  That sharp protrusion is great for 3D printing, as it makes it much easier to see these details on the printed model.

And the best part of this technique is how flexible it is.  Each of those veins is just a few vertices with edges between them and a few modifiers.  In fact, the way that this is set up, I don't even have to get my vertices and edges especially near to my model in order to lay them on there!  And, if I ever don't like the shape of some part of a vein, I can easily go in there and change it at any point, or even change the underlying model around!

So, how's this all tie together?  Well, the most important aspects are the Shrinkwrap and the Skin modifiers.  The Shrinkwrap modifier is the piece that lets me be lazy about the placement of my vertices, as it'll pull them inwards to the main object.  The Skin modifier is what makes those 2-dimensional lines into those nicely 3D printable veins.  So, let's look into this in greater details.

First, I made my core object.  If we ignore (and hide) the hole-filled outer membrane, that inner core is just a simple extruded cube with a Subdivision Surface modifier on it.  I used this as the core shape for drawing the holed-surface, but it's plenty for making the veins.  

After making my core mesh, I hit shift-A and added a plane, then in Edit Mode, I deleted all except for a single point.  With that point selected, I pressed e to extrude a new point, then clicked it into place.  I then extruded a bunch more points, creating the branching path that you see here.  When I wanted to create a branch, I just went back to that vertex and extruded the new branch from it.

After the basic shape was there, I added a Subdivision Surface modifier to round out those super sharp bends and give the later modifiers more points to work with.

Next, I used the Shrinkwrap modifier to bend my newly smooth lines onto the core object.  Notice that, in the Target field, I've selected my Outer-Membrane object.  That's what tells Blender what it should be pulling these vertices onto for this modifier!

Next, it was time for some 3D geometry!  That's done through the Skin modifier, which makes a nice blocky shell around those edges.  Of course, it's completely uniform in thickness, but that's easily solved!

Since I want everything to taper down at the ends, I selected all of those vertices via shift-click.  With them all selected, I went to the Transform panel in the top-right (press n if there's nothing there).  I then shrunk the Mean Radius X and Mean Radius Y values down really small; I liked how it looked at 0.07 for this model, but you do you!

The final step was to round out the veins, since I've never heard of one with a square cross-section before ;)  Fortunately, that's also super easy - just add another Subdivision Surface modifier to the vein object.  And that's it, one set of protruding veins is done!  To make more veins, I can either duplicate this object, or just start a new set of vertices & edges within the same object.