Tuesday, March 16, 2010
I just posted and updated version of the breed color charts on the website. It is still not complete, since there are colors (like Pearl and Dominant White) missing. I decided not to overhaul the charts now, since there will be so much more information in the books anyway. But I have tried to correct any outdated information, and add what new information would fit in the chart (mostly in the form of "extinct" colors rather than newly found ones).
at 10:41 PM
Monday, March 8, 2010
The only remaining pieces (aside from the large side) are the two back gusset pieces, which are tinted pink in this picture. These two pieces are designed to lift up with the casting, with the horse balanced on top like a pedestal. This is the way most horses are removed.
The two front gusset pieces came away really clean, so they didn't need an adjusting.
But while the first side came off easily and the two front pieces came away clean, the casting was still a little too soft to be considered leather-hard. Normally I would set everything aside at this point to let the casting firm up a little. That's because to break the seal on the other large side, I'm going to need to rock the casting a bit, and I don't want to risk collapsing the barrel, shoulders or chest. But since this casting is already lost, I went ahead and tried to remove it to show what happens when a casting is removed too soon.
Not only was my guy too soft to retain his shape as I jiggled him, the clay on the other side was still wet enough that it hadn't fully released from the mold. That pinned him in at the top if his shoulder and the point of his hindquarter. (You can also see the cloudy film the release residue has created on the surface of the clay.)
Here he is on the gusset pedestal, showing how pulling the casting while it was still pinned to the side pieces caused the piece to rip apart.
The two bits of stuck clay show where the casting had not yet dried enough to release from the mold. Fortunately it was the clay that was too damp, which is relatively easy to clean up with a fine (dry!) sponge. If the mold itself had still been damp, it might be impossible to completely clean the clay from the mold. Patience really is one of the most important qualities in slipcasting!
Even though my casting was badly damaged, I was still able to wiggle the two back gusset pieces free so that I could check for flashing. Sure enough, both hind legs had scraped clay showing where I needed to correct the molds.
It's hard to believe that a casting like this is a success, but it was because I was not after a usable bisque. What I wanted was information, and this first casting provided it. By looking at how the casting was going wrong, and adjusting the mold pieces accordingly, I was able to fix the mold so that future castings were easy to get.
Here is the second casting from that same mold, poured to double-check that I caught any potential problems. As you can see, the mold is clean and he came out whole, so I can declare this a working production mold.
at 8:48 AM
Saturday, March 6, 2010
I've lifted the first large side piece from my mold, so now I can start removing the inner pieces. The first one that comes off is the handmade neck-and-shoulder insert, since it partially covers both the ear piece and the first front leg piece.
Pieces are designed to be removed in a specific order, and to be pulled in a specific direction. For this one, it pulls upward and slightly to the right. (If it could have been pulled straight upward, there wouldn't have been a need for an inner piece, and the head and neck would have been included on the large side piece.)
The dark areas are where the slip seeped out the seams. This tells me that I mixed my slip a little too thin for this particular mold. I also have just a little bit of clay scraping on the forelock, so I trim those areas. The clay that seeped is cleaned off with a soft makeup sponge.
This is a good shot showing why the first casting isn't used. The white areas along the jaw, lower neck and shoulder are from the mold release. It usually takes one or two castings to remove the film the release leaves behind.
The next inner piece removed is the one between the ears, which I often call the "hat". Unless a horse has mane obscuring the ears, he always gets a hat. It pulls perpendicular to the ears, and this has to be done with care since it is really easy to take an ear off.
Each time I remove a piece, I am checking it for any areas where it is scraping off a layer of clay. When I find them, I use the hook tool to carefully trim the plaster flashing. Once the pieces are cleaned of any excess clay, the are reassembled alongside the other half. This is especially important with minis because the mold pieces are often small and easy to misplace. Once the mold has dried, pieces cannot be repoured, so a lost piece is a ruined mold.
Usually at this point, there are a number of options for removing the horse. Some separate out from the other large side piece, balanced on the remaining inner pieces. Sometimes a few of the leg pieces pull out first, then the horse and remaining inner pieces pull from the large side. Finn was designed to pull with all four gusset pieces still attached to the casting, but it turned out that the two front gusset pieces will fall off freely without removing him.
If I had been smarter, I would have seen this and designed the frontmost gusset (encompassing the chest and part of the front legs) as a "slider" that pulled away without lifting. As you can probably see from this and the previous pictures, there is an unfortunately placed mold key sticking up in the way. That's because I didn't realize this would work better. Molds are always like that; you see better ways after you have worked with them for a while. Even so, the front gussets on Finn tend to fall free with a little helpful wiggling.
That's good because the next part involves freeing the rest of him from the other side piece, and having his entire chest area to leverage makes that a lot easier. And anything that makes that part easier is a good thing, because it's the place most castings are lost. I'm going to lose this one on purpose, just to show why that is. (He is unusable as the first anyway, so he might as well serve as an object lesson.) I'll explain that in the next part.
at 11:33 AM
Friday, March 5, 2010
Having just finished a new plaster production mold, I thought it might be helpful to see how a new mold requires adjustments to work well. Production molds are made from the rubber master, but like anything handmade, each one is a little bit different. If I've learned anything in the last few years, it's that there are no perfect molds and each comes with its own quirks.
Unfortunately, you don't really know what you are getting until the mold has dried, which can take weeks. In the picture above, I've opened the new mold (for the drafter Finn) for the first time and am dusting it with a soft brush to remove any dust or dirt.
At this point I check the mold for obvious flaws like these bubbles in the mane. Textured areas like manes, tails and feathering are prime locations for these kinds of problems.
I use a small hook tool to remove and smooth casting bubbles. This particular mold only has the two bubbles. I've found that I rarely get bubbles with new rubber masters, but after a number of production molds the masters tend to pit. This pitting can result in bubbles in the production mold. Fortunately the problem is easy enough to fix.
Once this is done I am ready to pour the first test casting. This casting is not usable, since there is usually a bit of mold release still in the design cavity. It's sole purpose is to check the mold.
Here I have poured slip into the closed mold. Those straps holding the mold together are heavy-duty rubber bands. I need to keep it constantly full (like the top picture) because the slip in the pour hole creates the pressure the pushes the liquid up into the horse's legs. (Remember that the pour hole enters the belly, so the horse is being cast legs-up.) One of the hardest lessons to learn about casting is that this is not the time to multitask. Do not go do anything else! You will lose track of time and find the pour hole drained and (later) a horse without toes. Not fun.
The slip sits in the mold for a while, forming a skin. When I started casting, I wanted hard rules about how long the slip should sit. What was frustrating is that there were no rules. It depends on the mold, and the thickness of the slip, and the local humidity, and other mysterious factors I just haven't figured out yet. The only way to know it's time to drain the mold is by spilling a bit of slip out, and testing the thickness of the skin with a plastic mold trimming knife.
When the skin is the right thickness, the mold is turned upside down to drain. At this point you should have a hollow pony inside the mold - sort of like the model horse version of a chocolate Easter Bunny. (I have always wanted to put those yellow candy eyes on one...)
Here the mold is sitting upside-down on two plaster pedestals to finish draining. (The pedestals were made by pouring excess plaster into the bottoms of some plastic cups.)
Now there is more unpredictable waiting. The time it takes to get the casting to the right 'leatherhard' consistency is dependent on many of the same factors as the draining. Unlike the wait for refilling the mold, this is actually a really good time to multitask. Pick loooong chores. That's because no matter how soon you think the casting will be ready to demold, it is probably not ready. I hate to admit how many castings I have lost to my own impatience.
Molds are almost always designed to have a specific piece lift first. For Finn, the piece that I am holding is the first. I've taken off the rubber bands and removed the pour spout with the mold trimming knife (the blade is there just to the right), and am testing to see if it is ready to pull. When the horse inside is dry enough, the mold piece will pull, though there is often a soft "pop" as the suction is broken. If the side does not separate (at least a crack), the casting is still too soft.
It won't always pull completely free, though, at least not at this point. That's part of what this first casting is checking. There are almost always small areas along the seams where the plaster wants to grab the clay, and that will often pin the mold piece in place. The trick is to wait until the mold will crack open easily, but won't pull further. By carefully forcing the piece off, the clay will give and stick to the areas that need adjusting.
Here is that first piece with the tell-tale clay on the outer edge of the tail. Left as it is now, the mold will always want to hang there. When flaws like this happen in the wrong place, the demolding process can tear the casting apart. That's not likely in the case of the tail end, but leaving it would mean that part of the tail will have to be reconstructed each time since it would get scraped off with each demold.
It's better to just trim the excess flash from the mold so the tail pulls freely. Imperfections like this one are easy enough to fix.
But not all problems can be fixed. There is a chip in the piece along the shoulder (marked in the previous picture) that happened when the shoulder insert was broken from from the side piece. Fractures like that often happen where the sides butt up against a hand-formed piece. There isn't really a way to fix it, so each casting will have a larger-than-usual seam along that shoulder that will need to be trimmed. Fortunately trimming seams is pretty easy with greenware; far easier than with resin castings.
So now the casting is visible and I am ready to start removing the rest of the mold pieces. Like the first side piece, these are usually designed to come off in a specific order. I'll pick up there with my next post, starting with that inset shoulder piece that caused such problems when it separated.
at 9:49 AM
Monday, March 1, 2010
I have been dying to be able to announce these two new pieces ever since last Mayhem, when Sarah first showed them to us while they were still in progress. Sarah has more information about "Elsie" and "Oliver" on her blog, and as she mentions the two will be produced in earthenware here at Blackberry Lane.
These will be the first non-mini edition, and I am excited about the opportunity to work on a larger 'canvas'. I also have a soft spot for broodmares. When Sarah explained that she wanted to do a set that touched on the universal theme of motherhood, I was sure I wanted to produce them. Even so, I wasn't really prepared for how much these two really resonate with me.
Which is probably a good thing, because while their "story" makes my heart sing, that mare's tail is making my mold-making mind reel! I have no doubt that we'll get them translated into ceramic, but I suspect they will make for some interesting blog posts before it's all over.
at 11:07 AM