rock molds and modeling geology

Discussion in 'HO Scale Model Trains' started by Santa Fe Jack, Nov 3, 2006.

  1. Santa Fe Jack

    Santa Fe Jack Member

    As a geologist, I'll be paying particular attention to some extensive rock outcroppings and railroad cuts on my layout. I've been looking at some the rubber rock molds that are available, and some look to be good for this. But I'd need a variety of types, and the expense of buying them new from, say, Woodland Scenics, builds.

    So, I'm wondering, once people have built their layouts, and have used these molds, what do they do with them? Certainly they are fairly durable. Surely, not every modeler buys a new set of these molds just to be used a few times.

    Does anyone here have any used molds that s/he would be interested in selling?

    Another approach is to make my own molds, using real rocks and some sort of rubber molding material. Has anyone had success with this technique?

    I've been having lots of fun ideas about rocks -- modeling type localities (the geologist's term for "prototype") and marine transgressive sequences and the like. The cutaway back of the mountain could have fun things going on inside - a coal mine, a tourist cavern, a geologic radioactive waste disposal facility (my personal favorite). Any fellow geologists out there?
  2. Max

    Max New Member

    I ordered a gallon of latex from and expect it to arrive next week. It cost 36 dollars plus 15 bucks shipping. I've done a fair bit of casting from molds but never made one. I'll give you the details on how things turn out. Unless it becomes one of those episodes too terrible and unsettling to ever relate.

    These are the links I plan to use for info:

    I'm not sure if there is a geological term for ekphrasis or synecdoche, but do you anticipate being able to represent an HO shale cliff with a casting of a life-size piece of shale? I was just planning to cast some rocks to look like rocks, but I'd be very interested if you believe specific scaled localities can be accurately represented by actual examples.
  3. Santa Fe Jack

    Santa Fe Jack Member

    Max -
    I'd be very interested to know how the rubber molding turns out. I may go that route as well.

    That's an interesting and perceptive question about "ekphrasis or synecdoche". I've not heard those terms (from the study of Greek literature?) but I am guessing by what you say that you are wondering if a proper sort of similitude can be had by using actual rocks to represent rocks at vastly different scales. In other words, are rocks sufficiently fractal?

    Actually - yes, in many cases! In fact, a favorite field geologist's joke on an incoming class is to show a photograph of a rock, with a camera lens cap thown in for scale. Then - a second photo with the same "rock" and "lens cap", but with a person standing next to it, showing clearly that the "lens cap" is a huge mock-up, about a meter in diameter. The point is that rocks DO scale fractally. You can't tell from a simple photo with no other clues how big the rock is. Could be a hand specimen - could be an entire outcrop.

    Now, when it comes to specific rock types, some may work better than others. Shale actually might work well, using the edge of a hand specimen. My transgressive sequence would include shale, sandstone, limestone, which would be deposited as the ocean overtook the land. I could plausibly add some coal under the shale as well. This sequence could all be overlying some metamorphic or igneous rocks as well, or could be overlain by a bit old basalt flow, making a nifty caprock. I'm going to have fun with this!

    BTW, some of the link is missing, replaced by ellispses.
  4. zedob

    zedob Member

    Coal makes a good blasted rock.

    As for the "inside of the mountain", I believe the railroad museum in Boulder CO has a cut away view of a mine shaft in one of thier mountains.
  5. Rusty Spike

    Rusty Spike Member

    I used latex to create molds from natural cut sandstone that was used on my old farmhouse basement steps - it was an easy process (paint repeated coats of latex on the surface) and procuded nice results. The talent I lacked was in accurately painting the finished molds.
  6. Max

    Max New Member

    Jack, one of the intentions we have is to incorporate geology learning objectives. I've been discussing it with the science teacher; since we're doing the Baltimore to Ohio Valley most of the stone would be limestone, sandstone, shale and clay, and maybe a few other things like chert. Which ones would you figure are fractally scalable?

    Zedob, I'm planning to have part of a strip mine and a deep mine. A cutaway WV deep mine in HO scale would be difficult, but I'd like to see one.

    Rusty, I had expected porous rock like sandstone to be difficult for latex. It's good to hear it was easy. How many molds did you get from one gallon and how big were the molds?
  7. zedob

    zedob Member

  8. Collyn

    Collyn Member

    If you make molds from rocks add cheese cloth after the third coat it makes the mold a great deal stronger if its a big mold like the one I made. I put the cheese cloth in large castings as well, same idea as putting rebar in concrete
  9. MasonJar

    MasonJar It's not rocket surgery

  10. Santa Fe Jack

    Santa Fe Jack Member

    Yes, depending on the type of rock you are blasting. Coal breaks in an irregular fashion -- geologist call this conchoidal fracture. Same for glass and quartz, though the coal will be more interesting as it is full of small fractures and planes of weakness.

    This would be good for modeling a massive rock type, like a granite or a coal seam.
  11. Santa Fe Jack

    Santa Fe Jack Member

    Cool question. Most could be scalable, and it will depend mostly on finding a good specimen from which to make a mold. Simply use your powers of observation to see what looks right. I don't think chert will be scalable, though, since it occurs in thin layers in the outcrop, and hand specimens tend to be massive and glass-like.

    Another point is to get the layers in the correct sequence. The rock types you mention, limestone, sandstone, shale, and claystone, would be part of a transitional sequence from terrestrial deposit to marine, or vice versa, depending on whether the sea invaded the land or retreated from it. You will see all layers being deposited at the same time but in different places. As the strand (land/sea interface) moves, the deposits pile up, and you see the sequence move in space. For a given geographic location, then, the sequence changes as you move vertically through a section. Can you picture that?

    Working from the marine side inland, you would find limestones (deposited on the sea floor, either as a mass of remains, mostly from zooplankton, or perhaps associated witha coral reef) then the sandstones derived from the beach sands. Behind the beach you would have some muddy deposits, with maybe again a bit of limestones from algal mats. Inland, you get into more terrestrial deposits, which can vary a great deal. If you've got a thick marsh or swamp, for example, this would eventually become coal.

    Later of course, the whole mess could be folded and faulted, or eroded by later geologic action. If it gets buried deep enough, the whole pile will get metamorphosed, wherein limestone becomes marble, mudstone or shale becomes slate, and sandstone becomes quartzite. If you melt it all more, you get high end metamorphics, like gneiss or schist. These are half-way back to full melting, which is back to granite and other igneous rocks.

    Then, they all get exposed and worn down to sand again, and cycle continues.

    Every rock has a story to tell.
  12. Santa Fe Jack

    Santa Fe Jack Member

    Yes, that's a great rock for molds.
    Keep in mind the direction of the strata, however. In the phot there, they are near vertical, which means that the rock package was upended somehow. This indeed does happen in nature, of course. You'd want all the strata directions to conform.
  13. Max

    Max New Member

    Zedob, a horizontal or a slope mine might be a good idea, although I've never seen an HO scale model of those powered mine cars that haul the carts. The deep mines in WV go from a quarter mile deep up to several miles sometimes. So even a quarter mile mine shaft would be roughly 10-12 feet in HO. Be easy enough to compress part of it the way train layouts compress parts of the prototype, I suppose.

    Collyn, what do you think about using old shirts or maybe 12 gauge wire for support in a mold? I don't have any cheesecloth. I have a lot of 12 gauge wire though.

    Jack, that is some good info. I thought it might be possible to show the strata when the track passed through a cut. There might be room for a cliff that could show different layers of rock. Most of the cuts I've seen show different colors of rock but the texture hasn't been very noticeable, perhaps because the edges were all cut the same way. Usually seems to be lighter at the top then the dark red, black, and brown deeper in the mountain.
  14. jcoop1

    jcoop1 Member

    Got The Bug

    Well after reading this tread and the on linked to it I went out to the local TAP PLASTICS and bought a quart of thier Latex mold stuff. Just now I coated two small rocks with the first coat. In the morning I will add another and will continue to do so until I have at least 10-15 coats on them. A quart was a little over $17.00, I checked some online places that where a little cheaper but by the time you added shipping it was cheaper and much faster to just pick it up today.

    Wish me luck
  15. nachoman

    nachoman Guest

    Another geologist here - although I consider myself to be more of a "soft rocker". The biggest mistakes I see in model mountains and rocks are a lack of cohesiveness throughout the layout, or even within a single mountain. Many model mountians seem to look too "gnarley" to me to be realistic. I am guilty of that myslef, though!

  16. zedob

    zedob Member

    We need a geology thread. That, or a gallery just for rocks and such.
  17. Santa Fe Jack

    Santa Fe Jack Member

    I thought this was a geology thread.
  18. Santa Fe Jack

    Santa Fe Jack Member

    This is a good point, and I've had it in the back of my mind as I've been thinking about the geology that will underlie my layout. The entire layout is not very big on a geological scale, so the package of rocks under the whole thing should be of a unit.

    You know this, nachoman, so I'm just saying it for the benefit of others: The strata in a mountain are continuous underneath the rest of the layout, and may outcrop in other locations. If you've got a layer of tough sandstone running at a tilted angle through the mountain, then you might have outcrops of the same sandstone unit in line with the one in the mountain.

    One edge of my layout (I need to get some pix up) will have a long cutaway mountain -- about four feet long. It will have a railroad cut along the inside, having been blasted away to make room for a track. A roughly parallel track will run through the mountain, and the back of the mountain will be along the edge of the layout, cut off clean. Inside there I may put a coal mine and/or a tourist cavern (in a limestone layer) and/or a radioactive waste repository. Fun fun!
  19. nachoman

    nachoman Guest

    what area are you modeling, santa fe jack? Getting the colors right is also important.

    I think another key point to geology that is overlooked, is that the landscape is a prodcut of both underlying structure, *and* weathering and erosion. The best sedimentary strata I have seen modeled start with large, flat pieces of foam to get the overall grain to the landscape established. Then, detail such as rock molds are added to this base for detail.
    Also, the modeler should keep in mind the climate they are modeling. Certain climates can weather different rock types similarly creating a landscape that reflects the underlying structure very little. In other locations, shale beds form valleys and clffs are formed by limestone or sandstone units.

  20. Santa Fe Jack

    Santa Fe Jack Member

    I'm still trying to decide. I live on the Bandelier Tuff, part of the Jemez volcanic complex. Here's a URL with good photos:

    It would be very cool to model, and would fit well with the steep slopes that I will need to fit in track, but I think I want more variation, like some marine transgressive sequence that has been tilted up 30 or 40 degrees. Then I could do a coal seam (and a hard rock coal mine cutaway on the back) and a tourist cavern in the limestone, and such.

    Still ideas at this point...
    Doing the local geology is very tempting, replete with ancient cliff dwellings, petroglyphs, and ruins of old "Anasazi" communities. (I use quotes around "Anasazi" since it is considered disrepsectful around here to use that old derogatory word -- like "Eskimo" instead of the proper Innuit -- but I figured more people would know what I am talking about that way.)

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