I've collected some ideas and resources about creating pieces of crystal terrain for your miniatures.
Creating crystal terrain from non-transparent crystals
This is the easiest way, and it can look good from a distance. Actually, a real translucent crystal would look non-transparent at that scale, as light doesn't penetrate it that much.
Shaping foam: You can cut pieces of polystyrene foam into crystal-like shapes. This will give hard, crystalline edges.
Casting: You can choose crystal shapes (you can buy pieces of crystals from creative hobby shops and esoteric stores), and you can create plaster casts of them even in putty moulds. You can buy crystal shaped cake and chocolate moulds in supermarkets. If you'd prefer to cast in polyurethane foam, it's lighter and more durable, but you'd need to use silicone moulds. (If you use PUR foam in your chocolate mould, don't use it for what it was originally intended for, you should mark the mould, so someone who doesn't know this, wouldn't make a mistake.)
Sculpting from polymer clay: You can buy them in several colours, but you can even use paint to colour them to your liking. You can mix several colours in your putty, so you get different layers.
Buying: There are many crystal shapes on the gaming market, specifically made as terrain pieces.
When you have a shape you are content with, paint the whole thing in a dark colour, then highlight the edges. You can use several layers of increasingly whiter colour, until you reach white. Whether you should use glossy or matte colours, depends on your taste. A glossy finish makes the surface more reflective.
* * *
Creating a transparent layer on non-transparent crystals
Doing this is probably too much hassle, as it's probably easier to obtain materials for a fully transparent crystal and use those for the effect than build a non-transparent one and spend time on the transparency effect.
Cover a non-transparent material with transparent liquid polymer clay / acrylic medium / liquid epoxy: You can use a basic structure, like crystal shaped foam, and apply a thick layer of transparent material on it. The basic structure doesn't even need to get painted if you apply colours to the layer itself. It will make it somewhat translucent. For decoration purposes I've seen empty shells made of the transparent layer, but I don't recommend this for modelling.
Cover a non-transparent material with transparent plastic: You can set up and paint the basic structure, then glue acrylic sheets, transparent nylon, laminating sheets, or anything that will make it appear more transparent.
* * *
Creating crystal terrain from transparent crystals
A transparent crystal looks better, even though they are unrealistic in this scale. A transparent 1:50 miniature is practially as transparent as 1:1 glass.
Shaping hot-melt adhesive: Most of these glue sticks (for glue guns) are transparent, and they are soft. Gluing them into their final place is also easy, as you only need to heat them and push them into the intended place.
Casting: As mentioned above, you can create moulds. As I don't know any other transparent material besides resin, you'll need to buy or cast a silicione mould.
Crafting from plastic beads: I have seen plastic crystal beads in creative hobby shops to make necklaces or earrings. Don't let the customers waste them on such a vain fancy, buy all of them when you can get them cheap. There are also crystal bead hangers and curtain ornaments in house decoration stores, I've found you can get more beads at better prices. You can then put these beads into an air-dry putty or plaster base. One of the problems with these beads is that they tend to have a hole in their middle. To hide this, and to make them look more natural, I prefer to cut them into splinters.
Crafting from plastic crystals / plastic ice: These are an more ideal than beads if you can find them, as they don't have holes. You can find plastic crystals in house decoration stores and aquarium decoration shops. A similar material you can use are acrylic light diffuser sheets that can used to represent large blocks of crystal, or can be broken up into crystal shards.
Crafting from plastic forks / knives: You can get transparent plastic forks and knives cheaply. You can cut them up and create small batches of crystal needles and blades.
Crafting from decorative glass: You can find coloured glass pieces in home decoration and craft shops. These are already dulled, so you don't need to worry about sharp edges. The disadvantage of glass is that you can't change their shape as easily as a plastic one.
Buying: Although I can't recall seeing one, but there might be crystal terrain pieces made of transparent polystyrene or resin.
Although you can paint the outsides of your transparent crystals, they won't look as good and as transparent as if the colour is inside them. Also, paint can be rubbed off, so try to find crystals in the colours you need. For small clear transparent crystals it's useful to put the intended paint under them, and let the colour show through.
Whether you put shadows and highlights on these, depends on your tastes. If you'd like a realistic look, you should, as a miniature without shadows looks unnatural. As these crystal columns are already unnatural, I don't mind their otherworldy looks without further painting.
Basing them on a reflective, mirroring surface is a great idea (I've got from 18 Charlie), as it allows the light that gets through the translucent material gets reflected back, so it will look twice as good (well, 1,1-1,75 as good, but this depends on material of course). If you have chrome paint, you can paint the backs of your crystals and glue them anywhere to retain the reflecting effect. If you don't have chrome, even a reflective metallic paint may be better than nothing.
* * *
Resources - Creating crystal terrain for miniatures
Creating crystal terrain - Non-transparent crystals
RubbishInRubbishOut: Miniature Crystals Scenery is done .... kind of: Tutorial video on creating crystal terrain.¤
Awaken Realms: HD painting tutorial - How to paint magical, glowing crystals: Painting tutorial video on creating crystal terrain, using airbrush and paintbrush.¤
sandrartes: Translucents hollow beads- liquid polymer clay (liquid Fimo) tutorial: Tutorial video on creating and painting liquid polymer clay crystal shells.Ł
Creating crystal terrain - Non-transparent crystals - Using polymer clay
Stephanie Kilgast // PetitPlat: Polymer Clay Gemstone Crystals // Fimo Tutorial: Tutorial video on creating and painting polymer clay crystals.¤
Stephanie Kilgast // PetitPlat: PREVIEW // How to Sculpt Minerals/Crystals/Gemstones with Polymer Clay: Tutorial video on creating and painting polymer clay crystals.¤
Creating crystal terrain - Transparent layer over non-transparent crystals
Rainbow Lane: How To Make Alcohol Ink Pendants: Tutorial video on using metallic foil and paint to build up the inside of the crystal that gets under the glass or plastic.¤
Creating crystal terrain - Transparent crystals
18Charlie: The Crystal Fields: Tutorial article on creating crystal terrain, with showcase of terrain pieces.Ł
18Charlie: Easy to make Crystal Terrain (part one): Tutorial article on creating crystal terrain, using transparent plastic crystals.Ł
18Charlie: Easy to make Crystal Terrain (part two): Tutorial article on creating crystal terrain, using transparent plastic crystals.Ł
18Charlie: Easy to make Crystal Terrain (part three): Tutorial article on creating crystal terrain, using transparent plastic crystals.Ł
18Charlie: Internally Texturing Cast Crystals: Tutorial article on creating crystal terrain, using transparent plastic crystals.Ł
Creating crystal terrain - Creating moulds for crystal terrain
18Charlie: Making Crystals: Tutorial article on creating moulds for crystal terrain.Ł
18Charlie: Making a Small Crystal Mold: Tutorial article on creating moulds for crystal terrain.Ł
18Charlie: Making another type of small crystal mold: Tutorial article on creating moulds for crystal terrain.Ł
Creating crystal terrain - Creating moulds for crystal terrain - STL and Sketchup files
18Charlie: 3D Printed Crystal Files: Article with free templates for 3D printing.Ł
* * *
What do you think of these ideas about making miniature crystal terrain? Do you have further ideas? Tell your opinion in the comments!