Author: Marianne Hansen

We make molds for a lot of medieval gewgaws – roughly 525 items. Many of the smaller goods – spangles, buttons, chaplet decorations, belt mounts, clothing fasteners – come out of multi-cavity molds that cast three or more copies of the item.

It is important that the resulting castings are indistinguishable from one another except on very close inspection. We also want the mold to cast easily and completely (or nearly completely) every time. For this to happen, the mold cavities must be very similar, and they have to be laid out so that the metal fills each of them the same way. We try to choose the best mold design from a number of authentic layouts.

The two molds on the left are three part molds – the one to accommodate the button loop and the other so the stones can lie flat in the spangle mold while the metal pours in. The openwork star chaplet decoration mold and the bee spangle mold have cavities that branch off a central sprue. That middle sprue narrows as it descends and the lower feeds are narrower/thinner than the upper ones to balance the greater pressure to the lower parts of the mold. The mold for the triangular spangles equalizes the pressure in a different way, by arranging the cavities horizontally and splitting the main sprue to even out the flow and amount of metal to the various cavities.

This notebook page shows a layout we considered for the heart spangles, as well as some late sketches of the form the heart would take. (Preliminary sketches were on another page.) When we make round things we use a compass to lay out the pieces. But for items like the bees or the triangles – and the hearts – we employ templates to trace the shapes of the cavities. We have used cardboard and thin template plastic before; for the heart spangle Mac made a brass template to my final design. This let me trace the exact shape with a sharp needle on the stone – and also to trace the heart in pencil in my notebook to experiment with the beading, the loop, and so on.

Hours of careful work into the project, I was getting many of the cavities to fill, most of the way, most of the time. I put my initials and the date on the back of each spangle, so that any examples that cast fully could be cut off, cleaned up, and sold. At this stage we keep every casting for examination. Clipping off the good examples, we lay out what is left to show where the repeating problems are. In the shot above we see that of the six cavities there is still trouble with the upper two hearts on the right. The loops are not casting, and upper heart is not filling to the edge. I corrected only the places that were not working, leaving the rest of the mold untouched. The lighter areas of the mold show where I extended and deepened the back under the beading where it was not casting, deepened the loops, and reinforced the venting both front and back.

By the time I filled the stock box, the mold still was not working perfectly every time, so the next time I cast I will continue tweaking the cavities, the sprues, and the venting. I’m almost there.

The hearts themselves are also not perfectly identical – if you took a handful of them you could play “Spot the Difference” and sort them by mold cavity. But because I took care in design and layout, and worked as meticulously as I could, they are similar enough.

We used to offer a low-profile eyelet with three sewing holes and a pearled surface. It was copied after an original lacing eyelet in our collection. The eyelet was attractive and sturdy but the mold had problems.

There are several ways to arrange the cavities in a gang mold – and all have their uses. Marianne, who made the first mold in 2006, used a vertical sprue with individual channels branching out for each eyelet. The channels travel towards the outside of the mold, then drop vertically with the eyelet cavities all descending at the same angle.

If a gang mold is properly made all the cavities fill perfectly every time. If it is not, some cavities do not fill or fill incompletely. Meanwhile, other cavities flash (have “fins” of unwanted metal that sneaks between the mold parts) and have to be cleaned up after casting. The problem with arranging the cavities vertically in a gravity-fed mold is that the lower cavities cast completely at a lower temperature (of mold and/or metal) than the upper ones – or more consistently – because the pressure is greater at the bottom. Usually you can adjust the spruing and gates so that most of the castings are satisfactory most of the time.

This mold shows one way to try solve that problem – the upper branching channels are thicker than the lower ones, feeding more, hotter, metal to the higher cavities. Making the mold was a prolonged struggle, with repeated unsuccessful efforts to balance the pressure to each casting. It is also a tightly fitted mold and needed extensive venting. We were in the midst of a period of exploration of venting technologies, and Marianne vented it – too aggressively – with a grid of closely spaced vents across the entire back mold valve. The result was that, even after all the fuss, castings usually had fewer than four complete eyelets and many of the complete eyelets were flashy.

We continued to use the mold for a number of years, fiddling with metal temperature as we poured to try to control the flash; cleaning the flash off rapidly while cutting the eyelets from the sprue; throwing a lot of partial casts back into the pot, and cursing. We eventually introduced our pointy eyelets and let the filigree eyelets drop out of production.

The pointy eyelet mold is laid out on a different plan, with one sprue descending to a horizontal runner – and it worked well from the beginning. This arrangement equalizes the pressure to each cavity better, although you have to tweak the thickness of the runner to optimize it. This sort of mold is also sensitive to whether it is level when the metal is introduced, as a tilted mold may give you flashy castings at the lower end of the runner and incomplete ones at the higher end.

This week Mac remade the filigree eyelet mold on the same pattern as the pointy one. The new mold is also vented very thoroughly – those are vents straight through the stone (filled with copper wire) between each of the cavities – but more expertly. We know more than we did 16 years ago, thank goodness.

With the horizontal runner this mold consistently casts four perfect eyelets every time. We are offering this nice little lacing eyelet again.