• is wasting time before a medieval event this evening. #
• just did a search on "medieval pewtercraft" in google and was amazed by the results. #
• is away enjoying a time long ago, where mobiles didn't exist. ;) #
• enjoyed watching a friend and his Baroness get elevated to the Order of the Pelican. #
• is off to bed… #
• is back to looking for work. #

Finally!  it’ been a while since I posted a pewter project post, but I have now got a few projects on the go so there will be a number of them coming in the next month or two.

This weeks project has been a personal token for an SCA member to give to those they favour.   It is a simple medallion with initials on one side, and a raised representation of a logo/device on the other side.

Usually my medallions are carved into one side of the mould for depth and then the other side is smoothed and has the detail carved into that.  For this particular token I wanted to attempt a fully symmetrical moulding process by carving half the depth into each side of the mould.  I did this for two reasons, firstly, the one sided method I used previously whilst it makes for a nicer edge, usually needs alot more work to clean up.  Secondly it allowed me practice in aligning the two halves of the mould, whilst the old method allowed for misalignment, it meant that the main image was not centred on the finished token, and it would look kind of wrong.

After some experimentation in attempting to get a good quality pour each time (see last post),  I managed to find the best combination of temperature and mould tapping that resulted in a great amount of detail showing.  This further experimentation also made me realise the importance of the mould tapping and the continuation of it until the entire button* has solidified.  It seems that during the freezing process pewter can sill move past other parts that have frozen solid.  I suspect this would be similar to the crystals of ice that form in water, they allow water to pass around them, but still hold their shape.

Interestingly this also brings to my attention the creation of another type of artefact on an improperly cast item.  This artefact is caused if the mould moves during this crystallising phase of the freeze, and creates a texture like the one in the picture to the left.  It is rather a fine texture, however given the choice of all three of the artefacts described here and in the last post, I would rather this one, as the detail of the casting is almost perfect.  To reduce or even eliminate this artefact I would suggest the use of either wiring the mould together tightly, or using mechanical clamps to stop the mould from moving during the tapping and pouring process.  I may even attempt to make some sort of mechanical tapping/shaking jig so as to reduce stresses on the soapstone mould as well as the chances of the mould moving.

In a happy coincidence when I was checking the email to confirm that I had gotten the commission done as requested, I noticed that I was missing a vital part of the Dragons.  So the above information about the tapping/shaking process was only discovered after the wings were added, and the entire batch recast.  I’m sure my customer will be much happier with the better detailed casts than he might have been with the previous batch, specially as his Dragons are now actually dragons and not Lizards. ;)

* The “Button” is the larger opening in the mould where you pour the molten pewter.  It usually gets cut off and recycled.

It’s about time I got back to some real Pewter casting and the reporting of, so here’s my latest.  I have recently been working on a token commission and actually paid attention to the detail of the results of the castings this time, so I thought I would write about it in an effort to further muddle it through in my mind as well as help the one or two of you out there.

When casting there are two main problems that cause artefacts on the cast item.  The first is air pockets, and the second is pewter shrinkage due to the freezing process.  Unfortunately in period soapstone casting, the solution to one of these problems is also what causes the other, and a balancing act needs to take place to minimise both effects.

Air pockets can be caused by two reasons that I have been able to work out, though I believe the second is another issue which can be fixed separately*. The first is a lack of air escaping the mould before the molten pewter freezes, either by air flow dynamics causing restrictions in air flow out of the mould as the molten pewter enters, or the pewter freezing before it gets a chance to fill all of the detail.  This can be minimised by using a hot mould that allows the pewter to run into all detailed parts of the mould before it freezes, you may need to still play with the air flow dynamics on some moulds to ensure that the pressure of the liquid pewter entering the mould isn’t causing an air pocket in the mould to be trapped.

The secondary artefacts created when the molten pewter freezes and shrinks is a little harder to control, as the easiest way to control that is to have a cold mold and a quick pour of the molten pewter into the mould.  The cold mold freezes a skin of pewter allowing the detail to remain.  Freezing the pewter from the outside just a touch faster than it would with a hot mould this allow a harder skin to retain the detail whilst the pewter freezes and shrinks.  Another way to stop the shrinking from effecting your finished casting is to have a large enough sprue connecting the pouring button with the cast product so that there is enough room for the shrinking pewter to pull down more molten pewter from the button, however this is not always easily possible, as this sprue needs to large enough to allow the sides to freeze before the centre.

Another method of minimising the effect of shrinking on the casting is to rapidly tap the mould on a wooden surface as you are pouring the pewter.  This has the effect of increasing the pressure in the mould and effectively hammering the molten pewter into the details.  It needs to be done as you are pouring, and you need to be very careful as you don’t want to move the mould parts, or splatter molten pewter.

These details leave me with the conclusion that in order to get a perfect casting each time from a gravity fed, non-pressurised soapstone mould casting there needs to be a very delicate balance between the temperature of the soapstone mould and the temperature of the molten pewter.  If I were more serious about this process I would attempt to investigate this further with more period techniques for estimating the temperature of both mould and metal, however I believe that knowing that the balance exists and some means of minimising it’s effects are enough for me to continue.  The art of getting a perfect casting from each pour is one that whilst very rewarding, is not necessary with the ease of turning out pewter castings it is often better to do the best you can, and recast the ones that don’t work.  Of course, if it’s the techniques that are causing the artefacts in the first place, then these techniques do need to be addressed.

*The second cause is moisture in the soapstone turning into steam when contacting molten pewter.  This is easily identifiable as it looks like shiny inverted bubbles on the surface of the pewter casting.  It is also easy to avoid by pre-warming your mould before casting in an oven, however I find the easiest method is to just heat the mould over the heat source for melting your pewter, and then just keep casting in quick succession until it stops.