Alloys and Casting

So when it's all tee'd up and the wax was well and truly lost, It was time to try this alloy for the first time. As Recommended by Sylard, I've gone with a mixture of pure copper and then added 20% lead free pewter, in this case what I have is Rio Grands alloy that is >95% tin with a touch of zinc. Now my biggest problem in this was actually making the alloy up. I rushed it. Bad move on my part. The trick with this is that you have to melt all the copper (just shy of 2000'f) and then add the tin in which melts at 350-400'f.  Well, since I'm doing this with a torch and I only have two hands (where are minions when you need em?) this was a bit of a juggling act.  Swishing the crucible, which was a bit too small (which may well hasten my crucible making) adding the fiddly bits and trying to see if it was well stirred was  a big pain.   Next time for a more even mix, at least until I'm working in the pit, I'm going to make up the alloy in advance and pour it off into water making casting grain so that I can have it at least partially mixed and can melt up only what I need.   

Aside from that, the alloy did work out alright at least in part. It was a very liquid pour and filled well even if my mixing was downright bad.   So that bodes well for a more properly mixed batch.   The colour is good, I suspect it may be rather brittle in parts but I won't judge anything on this mix.   On both brooches the long part for the tongue catch did not cast, next time I will make them much more substantial and see how they cast. There were a few under-filled areas and a few gas bubbles in the bigger flat brooch.    I was pleased to see it hold the bronze well, even though there was a sizable crack down the side where the assembly seam was. 

Cast and quenched after the bronze lost its glow. The molds did not break up until I started striking them against the floor while holding them in the tongs.  The earthenware was fired through, though not particularly tough. It seems to have taken a good impression and the castings conformed well to it. I was able to break it up in my hands after it had cooled and the little bits that got trapped were no fuss at all to remove with a pick.

 You can see the bad pour on the top of the casting on the left, it took a few tries to get that one filled and get the metal out of my crucible.

I did a few swipes with a file to get a quick idea of the casting, the integrity looks good overall, a bit of flashing can be seen around the beak of the bird and the bottom half of the round brooch has a really rough surface.  All in all, it's a good step forward, I'm not sure I will take the time right now to do more than a cursory finishing, but I'll have a look again in the new year.

Waxes, Clay & Play

So beginning this step by step I want to test out all the various steps independently, so I can tackle each problem one variable at a time.  I've been reading through a mess of books and other resources keeping my brain stirring around the ideas and hunting for image sources for the oval brooches. To begin with the simplest things first, I started with how to apply the period appropriate pinback findings.  Generally these are constructed out of three tabs, two to act as a hinge and the third a bit longer to eventually be shaped to make a hook/loop. The designs I picked for the test cast are waxes things I've made in in the last year or so with a nice thickness and simple shapes.  The bird is my version of a style that was found in Sweden (Image: http://www.flickr.com/photos/32404172@N00/6735308883 , Museam: http://www.luhm.lu.se/Main_eng.htm ) and the round brooch is just a simple line and dot pattern.

 

Here's the finished and touched up waxes showing their sprue forms and then, below, there's some pieces of my local clay, wedged, pliable and ready to go.

 Two flasks ready to go, for the first firings I will be running these alongside a series of normal plaster flasks, the kiln firing for casting which is to ramp up in stages to 1300F and then back down to about 1000 to cast over the course of 6 hours.

Now the next wee adventure, there's much to be said for working in the right materials.  So I poured out a sheet of beeswax about 3mm thick.   I then transferred a rough tracing of the design to scale, on the wax by drawing over a piece of paper placed over the wax and tacked down in place. 

This, when finished will be a replica of a belt end strap very much like this... " http://www.britishmuseum.org/research/collection_online/collection_object_details.aspx?assetId=968329&objectId=64687&partId=1 "

Building up the wax where the heads and beads will go gives me a good layout and helps the detail lines fall into place.  I'm not inclined to obsess over each and every line but I'm getting the feel for this.

 The wax was a bit gummy and would have been easier to work on if it were a bit colder, but it's now at a place that's good enough to try out some impressions.  I've kept the design free of undercuts though if there are small ones the clay will actually be fairly forgiving, there's really nice plasticity in this earthenware.

 Pretty good transfers in these, a few touch ups on the high points and a retracing of all the linework.  At the same time I melted up some of the some more wax and formed a bowl for the first of the simple brooches that I want to carve, these are large beasties, about 11cm x 7cm. 

 Wax #1 is a mess, the sides were pulling in too much as it cooled, so I messed around (a bit too much), but things get better on the next pour.  I pushed out the sides about 1/2 cm all around to give more allowance for shrinking.

 Then, I did a clean pour and additionally to help fight shrinkage, I kept dripping wax into the middle without breaking the meniscus. 

 A collection of all the pulled waxes.