Mister Beasley... "Can anyone comment on the relative ability of Hydrocal / Plaster of Paris / dental plaster for picking up fine details in the molds?" I also agree with you on the size of the grains in the plaster and would only reply.. "You think a Dentists wants a grainy 'impression' of someone's teeth"?
But in answer to your question.. I can only tell you what I know.. and what I do.
I do have the Bragdon molds..
'
with a ruler to see the actual size.
and the numbers and prices.. $15.. $18 and $25.
'Surface Tension' yes.. that is what is keeping the plaster really getting into and adhering to the mold. Even though your plaster mix has been mixed correctly with no bubbles.. you can and will still get an impartial filling of the cracks and detail.
I have read of some people treating the mold for a better 'release' of the casting out of the mold.. but I really frown on it. I dont' think that is my approach. Besides.. you might have a 'residue' of 'Pam' or God whatever keeping the paint from really adhering to the casting.
I truly believe that all you have to do is 'wet' your mold down. Then really dry it. Smack it on the table. Get all the moisture you can see off the mold. What has taken place.. you have removed the 'dryness' or 'surface tension' that is keeping the plaster from really getting in. Think about the casting.. its clean with no 'Pam' or whatever on it.. keeping you from painting it correctly.
Then I use a paint brush.. and paint the plaster into the fine cracks and detail of the mold. When painting the plaster into the mold.. I find I have no air bubbles.. and can apply a thicker coat afterwards.
Then I apply small cloth strips over the 'high' area's of the mold. You know the jagged parts of
the mold that will stick out. (on the backside of the casting)
Yes.. that is the weakest part of a mold.. a thin mold approach that I use. Then apply one more coat of plaster.. followed by one big patch of plaster cloth to the mold.. for added strength.
The finished product.. is an extremely thin .. light.. very strong casting.
My latex molds.. are very flexible.. and would suggest always to keep them out of the sun.. or light for that matter.. I used latex rubber bands to hold the mold around the flashlight.
The other side of the flashlight mold.
This is the result of using a flashlight.
You can use various object to obtain many different rock faces.. to obtain.. a curve.. a gradual incline... or what ever. Just pick up anything.. and tape it to your mold.
A bowl is a good one... lol.
How bout a bannana? lol
I even took pics to see how much detail there was.. and how easy it was to pull Dental plaster out of the mold.
After I was done.. I noticed how thin, light and how strong the casting was.
Side note: I can even break this casting a bit.. remove certain areas.. it breaks nicely.. and the plaster cloth on the back holds everything together.. so I can go back.. add plaster to the areas.. to seal them up.. and I guess its a mild re-glueing with plaster. I know this.. If I waited until the next day.. I would not be able to break it up.. its that strong.
One slight side note: after you are done with your casting.. go back to your mold.. and wash it off.. with water.
The longer you take to clean your latex mold.. the harder the plaster becomes.. and the harder to clean.. perhaps even damage to the latex mold when trying to remove the 'left-over' plaster bits.
AS far as your question goes as far as detail.. well I used the WS paints .. and this is my first time at it.
I am happy with the detail.. and this is the best shot I can show you.
Now for my last pic.. just a side note.. but someone out there might want to know.
Mixing plaster.
1. Pick a smooth bowl. Why?> When you're done.. and the plaster is dried to your bowl.. just add water.. look closely at the bow.. you'll see a thin film of plaster.. that just slides up and off the rim of the bow. If you pick the wrong type of bowl.. you'll have problems cleaning it. This just take 10 seconds to clean.
2. You see the way the spoon is? Well mix your plaster exactly like this. End result is less air bubbles. I don't know why.. I guess.. when you stir the spoon.. as it is in the pic.. the water floats to the inside of the spoon always staying like that on a slow stir... while the rest of the plaster is being mixed under the spoon. But in my honest opinion you cut down on the bubbles.
Now I don't claim to be an expect.. but only one that wishes to share what I know and what I've done... perhaps it might spark other ideas that lead to better ideas.
Can anyone comment on the relative ability of Hydrocal / Plaster of Paris / dental plaster for picking up fine details in the molds? I suppose this would be determined by the size of the dry grains. I have some really nice molds which give great results with Hydrocal.
I've also used Bragdon Foam with a Bragdon mold. This gave very nice results, too. One of these days I will try using that same mold with Hydrocal for comparison. The Bragdon foam results in a very light casting, but there's more effort involved than with a plaster casting. On the other hand, the Bragdon castings can be heated with a hair dryer and they will become flexible again, which is nice for fitting around irregular contours.
It takes an iron man to play with a toy iron horse.
Tom, I say... both.. and neither... lol.
Ah to make this very short. I use 'Dental Plaster' its cheaper.. and I believe the same as Hydrocal. Densite is the name.
But in short... using the hyrdrocal/dental plaster. Its stronger. Way stronger. I pour less.. and use a clothstrip on the back for added strength. I use less plaster.. pour a thinner mold.. and is light.. but strong.
Example: I had poured a tunnel portal using the dental plaster. Left it sitting on the edge of my work table. Well, the thing fell off the table and landed on the tile floor. "CLANK" was the sound, a high pitch clank. I picked it up off the floor.. looked for chips.. cracks.. nothing. Then I knew.. I'll never ever use anthing else.
Now all I do is, just paint a 1/4 thickness of plaster.. lay in a cloth strip and done.
Not the best photo.. but study this sheet.. I believe it helps.
I have poured large faces of rocks.. using less and less dental plaster.
Of course this is the backside.. but its to show you how thin. Good luck.
Thats it.. btw.. I picked up my Dental Plaster off of ebay.
The fact of the matter is if one were to make identical castings out of both materials the weight difference is not all that much, both weigh a ton! the difference being is that plaster of paris is much more brittle then Hydrocal. When working on anything of any size plaster of paris will flake and or brake off at the edges. Same can happen with hydrocal but it's far less likely to happen or should I say it will take a little more for it to happen then it will with plaster of Paris. Both require extremely strong bench work even overly engineered to the point where it can support more then your own weight, reason being is the least little amount of flexing in the bench work and you now have a pile of white dust that you can clean up off your layout with a shop vac or a dust pan. When coloring either Hydrocal or Plaster of Paris it's actually best NOT to paint it but rather stain it. Strictly my O/P as some doe paint hydrocal to seal it first. It's natural tendency is to suck up stains or washes etc. like a sponge. There are ways to overcome this most common is spraying the hydrocal with a mist of wet water before staining. This helps slow down the absorption process. When you stain things like hydrocal walls tunnel portals etc. you get far greater detail then you would by painting. The pictures below are of a Hydrocal High Arched PRR prototype stone viaduct that I've been working on the past week or so. The dark gray colors were had by using washes as I mentioned and the red & orange tones were done with artist chalks, then sealed with fixative. Sorry for the poor picture quality but the reddish color of Pa. Stone is not really well represented by my poor photography.
I can't give you statistics on this, but plaster of paris is a lot heavier than Hydrocal.
Alton Junction
I have used both and I color my rock castings with diluted acrylics. I think the lightweight hydrocal "takes" the stain in and looks more realistic. Just my opinion...Tim
A true friend will not bail you out of jail...he will be sitting next to you saying "that was friggin awesome dude!" Tim...Modeling the NYC...is there any other?
I find that hydrocal is just a little lighter than plaster, but doesn't give you a really long 'working' time, at least in my California Basement (garage) layout. But it is awfully good for rock castings. Light and strong.
Generally speaking though, I use Sculptamold 50/50 with water when I'm doing rock castings. It's a slower method and takes longer to set up, but I like the results. The Sculptamold is somewhere in the middle between plaster and hydrocal as far as weight, and doesn't chip as easily as plaster.
But all three DEFINITELY have their uses.
Tom
Tom View my layout photos! http://s299.photobucket.com/albums/mm310/TWhite-014/Rio%20Grande%20Yuba%20River%20Sub One can NEVER have too many Articulateds!
I find Hydrocal is better for making rock castings. Plaster of Paris (Hilton?) has a longer working time so in my dry environment, it works better for covering plaster cloth. I prime neither when painting.
Micro Mark has a very attractively priced Hydrocal offering (compared with WS).
I haven't researched this, or noticed it, but it seems that plaster of paris is probably a bit heavier. It might add up over many castings applied to a significant layout, but I'd bet it doesn't add up to more than maybe five or six pounds once it is dry and in place on most layouts.
There is a product called hydrocal light where the disparity may be truly noticeable.
Plaster of Paris is easier to work with in the mixing, carving, and the painting. Hydrocal doesn't take paint easily. It would do so after priming.
-Crandell
I have tried both. To me plaster of paris is easier to work with and cheaper. However I've heard comments that it is to heavy. Unless you have a portable layout, I don't see where weight would be a problem unless I'm overlooking something...comments?