Thanks to everyone who responded to my question about replicating stranded steel cable. All great ideas. Greg Amer pointed me to the 'Beadalon' bead-stringing wire from Michaels. It worked perfectly Greg!

The prototype:

I find when securing real dirt with a 50/50 mix of matte medium and water the dirt shows to be darker when it dries.  Is there anyway you have found to prevent the color change? Hair spray will work but is not strong enough for the initial application of dirt but works fine for adding foliage on top of it.  Paint will also work but seems to only hold a very thin layer of the dirt.  Is the only answer to start with a lighter color of dirt to begin with?

Any other suggestions are more than welcome.

MRH: Because this site repeats the first post across all the thread pages, long initial posts aren't the best. We dramatically shortened your opening post and moved all the good stuff to the FIRST COMMENT, which is a best practice on threads here.

Earlier this month I received a couple of photos from my friend Brian of the Kankakee River Bridge that I had designed and printed for him.  I gave him a pile of parts (2nd batch shown, parts for three spines delivered earlier):

And then I said, using my best Hedley Lamarr voice:  "Now go do your vodoo, that you do, so very, very well!

Here is what came out. sitting in its final resting place on Brian's layout: