Author Topic: casting rocks  (Read 10042 times)

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tom mann

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casting rocks
« on: January 01, 2007, 09:04:17 AM »
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I bought a few woodland scenics rock molds.  Any tips for me? 

tom mann

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Re: casting rocks
« Reply #1 on: January 01, 2007, 10:38:19 AM »
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hmmm...I think I should have mixed some color in with the hydrocal...

wm3798

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Re: casting rocks
« Reply #2 on: January 01, 2007, 10:58:25 AM »
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#1 - Don't use their "lightweight Hydrocal"... It's crap, and crumbles while you take it out of the mold.

#2 - Yes, add some color to the plaster mix.  Powder tempera would probably be best... I've tried using craft acrylic, but it extends the drying time a bit.

#3 - take the bigger castings and break them into chunks before installing.  This enables you to use the same mold several times, but still vary the appearance.

Lee
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Lee Weldon www.wmrywesternlines.net

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Re: casting rocks
« Reply #3 on: January 01, 2007, 11:23:40 AM »
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#1 - Don't use their "lightweight Hydrocal"... It's crap, and crumbles while you take it out of the mold.

Hmmm, I've cast hundreds of rocks with both the WS and my home made molds using the lightweight Hydrocal and have never had a problem with it crumbling. Are you spraying the mold with soapy water first? I wet down the mold with a fine mist of soapy water (about a teaspoon per quart) just before casting and let the Hydrocal dry overnight and the rocks just pop right out.

As for coloring when mixing, any kind of paint can interfere with the cure and weaken the plaster. Try some concrete coloring pigment. (Home Depot, Lowes, etc. carry it) Just a tiny little pinch of it goes a long way

For coloring afterwards, try any kind of water based wood stain. The lightweight Hydrocal is very porous and the stain will soak in fairly deep so it will prevent those glaring white spots if you get a little scratch or nick in the surface of the finished rock.

Iain

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Re: casting rocks
« Reply #4 on: January 01, 2007, 12:30:16 PM »
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Here is something that my dad does, something he learned from a fellow model railroader:

Have a jar of paint thinner dedicated to cleaning brushes used for weathering AND metallic paints.

Whenever the paint thinner runs low or the level of 'gunk' gets high, use the paint 'gunk' in the bottom of the jar to stain the rocks once the plaster is dry.

The weathering colours give a nice base colour to the rock, and the metalic colours leave spots of mineral deposits.

After this has all dried, drybrush with various colours to match the rocks in the area you are modelling.

Add some very fine gloss black and silver streaks to represent mica, if apropriate.
Thanks much,
Mairi Dulaney, RHCE
Member, Free Software Foundation and Norfolk Southern Historical Society

http://jdulaney.com

tom mann

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Re: casting rocks
« Reply #5 on: January 01, 2007, 03:45:29 PM »
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Well, this is my first rock  ;D



Nothing really special.  Just casted with white and then painted with a very thinned wash of titanium and raw umber.  I followed that up with a raw umber wash to bring out the detail in the crevices.  If I could do it over again, I would mix some paint in with the Hydrocal.

tom mann

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Re: casting rocks
« Reply #6 on: January 01, 2007, 03:50:30 PM »
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rock #2:



 :D

John

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Re: casting rocks
« Reply #7 on: January 01, 2007, 04:05:55 PM »
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Cool .. keep going .. I need about 100 more  8)

Ed Kapuscinski

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Re: casting rocks
« Reply #8 on: January 01, 2007, 04:27:27 PM »
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I don't like you getting into scenery. That's my thing.  ;D

Craig Martyn

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Re: casting rocks
« Reply #9 on: January 01, 2007, 04:31:14 PM »
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Looking great Tom!  They have a very "Mormon Rock" look to them and I love that...

http://www.railpictures.net/viewphoto.php?id=166939

Now all you need is an entire Cajon Pass layout to use them in!  (Geeeeeeeeeze that would be sweeeeeeeeet!)
Craig Martyn
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Chulvis

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Re: casting rocks
« Reply #10 on: January 01, 2007, 04:33:00 PM »
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They look like real rocks to me.



Red Rock

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Re: casting rocks
« Reply #11 on: January 01, 2007, 04:47:47 PM »
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Looks real good Tom. I don't remember seeing much like that around the LA river though? ;)
Red Rock

tom mann

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Re: casting rocks
« Reply #12 on: January 01, 2007, 05:49:46 PM »
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Looks real good Tom. I don't remember seeing much like that around the LA river though? ;)

maybe before they paved it.

wendell camp

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Re: casting rocks
« Reply #13 on: January 01, 2007, 07:03:13 PM »
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Tom all I can say is ROCK ON ::) ::) ::) ::) ::) :P :P
wendell   NHRA#59

wm3798

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Re: casting rocks
« Reply #14 on: January 01, 2007, 10:21:07 PM »
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I wonder if you shot the raw plaster rocks with a spray primer, then just worked your weathering magic as you do on other media, if the results might be less "white".

I'm trying to simulate the browns and tans of the loose shale in western Maryland, and my rocks keep coming up too pale.  I think I'll try some of that tomorrow...  (I'm taking the day off!!)

Lee
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Lee Weldon www.wmrywesternlines.net