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Post by miltonmurphy on Dec 1, 2013 4:31:32 GMT
Hi all...I've never used Hirst Arts molds before. I like the idea from Scotty of using select molds to jumpstart a craft. In my case I'm doing a bar/gambling hall sort of place and was thinking of getting the tavern/inn mold for bottles, plates of food, etc. so I can concentrate on the larger items. Was hoping to get some info in two areas. Have others used these molds as "supporting cast" (see what I did there? ) in crafting before? Was it worth it? Additionally I'm seeing a lot of discussion on dental plaster and what not being better than typical old plaster of paris. The rub is that it's expensive (doubling the price!) to get that stuff shipped since I cannot find it locally. For those that have done this sort of thing, would regular old plaster of paris from Ye Old Big Box Construction Store work? Cheers, MM
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Post by skunkape on Dec 1, 2013 4:43:34 GMT
I've got a lot of Hirst Arts molds, some "supporting cast" molds and lots of others. I have found there are 2 main problems with plaster of paris, 1 it takes forever to dry and 2, it's very brittle and breaks easily! I broke down and bought Merlin's Magic from Clint Sales, which is located in Mass and had them ship it to my house in Florida. I'm very happy with it and will be buying another box of it before to much longer! Not sure where you're located, and your cost will vary. You can find five suppliers in the U.S. by going to the Hirst Arts site, here. Personally, I really like Merlin's even with the cost. To me, the less time it takes to cast and the stronger it is, it's worth the cash! I just realized I didn't answer your question! LOL. Yes, I think getting certain "supporting cast" molds from Hirst Arts would be worth it.
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Post by adamantinedragon on Dec 1, 2013 4:56:24 GMT
Milton, I have been doing Hirst blocks casting for about two years. Here are my thoughts.
1. You need to find some way to get the superior plaster products. Plaster of Paris itself is too soft and fragile. I use Hydrostone. It took me a couple months to find a local supply, eventually I found a place I could buy Hydrostone at a ceramics supply store. I must have made two dozen calls before I found a place. I buy 50 pound bags of Hydrostone for $35 each.
2. Casting is a skill, like many other craft skills. The more you do, the better you will get. In general casting larger, less detailed items is easier than casting smaller, more detailed items. The items in the Hirst tavern/inn accessory mold are among the smallest and most detailed items you are likely to ever attempt to cast. If there is one mold I would not recommend for someone to start with, that's the one I would pick. I would recommend that you buy one of the general block molds and work on that until you get comfortable that you have figured out how to cast well enough to attempt the tavern accessory mold.
3. If you are determined to pursue casting with that as your first mold, you will need a crash course on quality casting. The things that are going to be hard will be getting your mix right, mixing it thoroughly without bubbles, pouring it into the mold so that you don't create bubbles, vibrating the mold to remove inescapable bubbles, and scraping the mold to get a smooth, consistent cast. All of those will require skill.
If you have cast with resin before, that will help you, but plaster is more finicky than most resins. Plaster is more of a suspension than a solution when you pour it, if you have the mix right it will be thick and will likely contain a few lumps now and then. To get it to pour smoothly out of your cup you'll need to develop a technique of tapping or vibrating the cup as you pour, that will greatly facilitate the ability to get a thin enough stream to get into the tiny openings for the tavern accessory mold.
But before you even begin to mix the plaster, you need to create some "wet water", which is a solution of a drop or two of dish soap in a quart or so of water. Shake that up and let it sit so that it is good and mixed, then put it in a small spray bottle and before you mix the plaster, spray the mold thoroughly with the wet water, tapping and spinning it to get the solution into every crevice and cranny of the mold. That will tend to "pull in" the plaster mix and will do a lot to reduce bubbles. Some people use a mixture of "jet dry" and claim it works best, but I've always used dish soap.
When you pour the plaster you'll have to pour a thin stream, and keep it going or the plaster will start to thicken on you. You don't have a lot of time to work with plaster once you've mixed it. So you will probably mess up a few molds until you get the muscle memory in place to move smoothly from task to task. Pour the plaster as close to the edge of the item's cavity as possible, in fact it is sometimes best to pour the plaster on the divide between two cavities and let the plaster flow down the walls. If you pour directly into the cavity, some of them are so small or thin that you will just create a giant bubble that you won't even be able to see until you demold it.
Once you have the plaster poured, you'll have to bang on the table to vibrate the mold. That will jar reluctant bubbles loose and improve your casting quality. Some people create "vibrating tables" for this purpose. I use a small vibrating plastic device I took out of a teddy bear our dog chewed up. (Insert gratuitous "adult humor" joke here.) Once the plaster has been poured, I put the vibrating device on the table for a short time on all four sides of the mold. Once you've completed that, then you can scrape the top of the mold with a plastic ruler or something. Just be sure whatever you are using is completely flat and wide enough to cover the entire mold. Scrape the excess to the side for now. After you've got the hang of all this you might be able to salvage that excess plaster for some other purpose (like tossing it into temporary clay molds, like I do).
I have dozens of casts from that mold. I would say that even with my fairly extensive experience, it is rare that I cast the entire mold without at least a couple of items ruined due to bubbles I could not entirely get rid of. But if you cast it enough times, you'll get what you need.
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Mike H "Chugosh"
Cardboard Collector
Dabbler, Builder of stuff, some of it even is terrain.
Posts: 28
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Post by Mike H "Chugosh" on Dec 1, 2013 5:56:52 GMT
Fantastic pointers, sir! Thanks!
I am lead to ask the derailing question of how does resin fare in the Hirstarts molds? Seems like a much better thing than plaster for the itty bitty bottles and whatnot. Maybe even an expanding foam for the bigger stuff--maybe not so bright for open molds I guess.
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Post by adamantinedragon on Dec 1, 2013 6:28:24 GMT
I've done a couple of resin casts in the Tavern accessory mold. As a general rule Bruce Hirst discourages using resin in his molds. The resin will break down the silicon mold material much, much faster than plaster will. But you should still be able to get several good casts even using resin. The truth is though, that even with resin I was having some bubble problems with that mold. It really is a difficult mold to master.
To give some idea of the effect of resin on silicon molds, I had a custom mold I made with a slightly softer mold material than Hirst molds use, and I was able to get about a dozen highly detailed resin casts out of it before it started breaking down. Now, that was a much more difficult mold than even the Hirst Arts molds, with some long crooked fingers involved, so you can probably expect ate least twice as many casts using resin out of the Hirst molds. Maybe even more.
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Post by miltonmurphy on Dec 1, 2013 18:29:50 GMT
Thanks skunkape and adamantinedragon. I've done some extensive reading and viewing of online tutorials so I get where you're coming from. I appreciate the information and especially the point about starting with another mold with larger pieces to get the hang of it. Will definitely look around town (I live in New Orleans so a lot of the places listed on the Hirst site are far, far away shipping-wise. Even the closest one in Arkansas still doubles the price for shipping.) Cheers, MM
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Post by skunkape on Dec 1, 2013 19:45:19 GMT
When you started talking about bubbles in your casting adamantinedragon, it reminded of a debubblizing agent I picked up after seeing it talked about on the Hirst Arts forums. While I haven't used it yet, Almore, Debubblizer Surfactant is supposed to get rid of most bubbles when casting! Even on the smaller pieces and with out a vibration table!
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Post by adamantinedragon on Dec 1, 2013 20:03:39 GMT
When you started talking about bubbles in your casting adamantinedragon, it reminded of a debubblizing agent I picked up after seeing it talked about on the Hirst Arts forums. While I haven't used it yet, Almore, Debubblizer Surfactant is supposed to get rid of most bubbles when casting! Even on the smaller pieces and with out a vibration table! Skunk, that does the same thing as the jet dry or the wet water. There are two kinds of bubbles to deal with, surfactants help with bubbles that are created by surface tension on the mold causing the plaster (or resin) to flow around spots in the mold instead of flowing across it. The other kind of bubble is formed when you pour the material into a small area and you capture a bunch of air underneath the plaster. Surfactants don't help with that sort of bubble. And those bubbles are easier to create the smaller the mold opening is. The Tavern accessory mold has a LOT of very tiny items with openings just a few millimeters wide. It takes a lot of practice to figure out how to pour your plaster or resin in such a way that you avoid creating those sorts of bubbles. If you use wet water, pour smooth, thin streams, use a vibrating table and avoid creating bubbles by catching air in the flow, you'll do fine. My point is all of those things are skills that you develop.
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Post by skunkape on Dec 2, 2013 1:37:20 GMT
Oh, I know about the jet dry wet water, this stuff though is supposed to be better for breaking surface tension. Didn't realize you were talking about bubbles from pouring, yes that's a totally different problem!
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