Help staining rocks

[tbdanny]

Hi all,

I've just tried staining plaster rocks for the first time, using very watered-down artists' acrylic paints.  While I'm generally happy with the results so far, there's something that's bothering me.  In the two photos below, you can see spots on the castings where the stain just hasn't gone into the plaster.

I have already tried scraping the bits that refused to take the stain, thinking that there was something on the surface, but to no avail.  The plaster used a mix of water, vinegar and white glue mixed 1:2 with the plaster.  Any advice on this would be appreciated.

Thanks in advance,

tbdanny

[Phoebe Vet]

My bet would be that the white glue did not get totally mixed.  That stuff is pretty heavy.  Why did you add it?

I mix my rocks just the way it says to on the package.

 The light spots are not a defect, they are areas of Ocher and Burnt Umber that I put on before the black.  Everything is diluted about 20 to 1.

[cowman]

I have never heard of adding the white glue either.

However, look at real rocks, they vary a lot expecially large ones.  I have a spot in a ledge that the caulk holding a plaster casting on shows through (whoops).  Will take a little glue, ground foam and create some vegetation growing out of a crack in the rocks.  For larger spots put on a light coat of glue, fine ground foam, "voila," moss grows on the rock.  Sounds like an easily covered problem.  Would reconsider adding the white glue, unless you know it has a purpose that we don't.

Another thing you can do is add color to the plaster mis.  Makes it so even if you get a chip in the plaster, it doesn't show through as a stark white spot.

Good luck,

[dehusman]

Paint your rocks with flat latex paint, the base rock color then apply stains.

Or paint your rocks flat black then drybrush to lighten them.

[CTValleyRR]

Here in New England, our rocks have large chunks of quartz and calcite in them, which create natural white streaks and spots, some of them as big as a car.  That doesn't necessarily look unnatural (depending on what you're trying to model.

I would agree that if you must cover it, use a full-strength acrylic or latex paint, or disguise it with some suitably placed vegetation.

 

[rrebell]

I use just plaster, no white glue, no vinegar. You are trying to over engineer this stuff.

[tbdanny]

The white glue I added following a previous post on this forum:

http://cs.trains.com/TRCCS/forums/p/171192/1878980.aspx#1878980

Looks like I'll have to toss what I have and start with non-white glued plaster.  Thanks for the advice, all.

[gandydancer19]

I just looked at the link.  Adding white glue is new to me too, but for fragile parts, it make sense.  However, to me, rocks are not fragile.  If I remember correctly, the vinegar is added to slow the cure time.  I usually add salt which makes it cure faster.

Even without the white glue added, the stain is going to be different shades on different places.  This is normal and natural.  For those spots that are really white, you can just paint those areas.