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discolored Pewter after casting

Hey everyone,

I can't imagine that this question hasn't been asked before, but I must be using the wrong keywords. 

I used a small electric crucible (for lead and pewter) to heat up pewter and pour it into a coin shaped plaster mold.  Truthfully, I'm pretty pleased with the level of detail, but I've got some 'burned' colored discoloration on the coins.  I've tried gently washing with soap and water which got off some of it.

1) am I doing something wrong to produce that coloring?
2) will silver polish clean it up, or will it damage the pewter?  (almost certain it will be fine, but thought I'd double check) Should I just be scrubbing harder with soap and water?

For whatever reason, the image uploader isn't working.  I'll try to get one into the comments after I post this.

many thanks!

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Kiteman3 years ago
According to the Pewter Society:

In daily use, pewter was kept bright and polished and some collectors prefer this appearance. Pewter does not tarnish like silver, so a periodic clean with an all-purpose metal (not silver) polish will keep it looking bright.

Much old pewter is patinated and has a colour ranging from mellow silver to charcoal grey, a more ‘antique’ appearance favoured by many collectors, especially in Britain and Europe . It is possible to restore patinated pieces to a brighter and polished condition and there are degrees of restoration depending on whether a completely untarnished appearance is preferred or whether some signs of age, e.g. oxidation in joints, dents, etc., should be apparent.

Oxidation on pewter varies according the composition of the alloy and even this composition can vary on individual pieces. Serious oxidation can eat right through the metal and eventually create holes, especially in sadware (dishes and chargers, for example). Expert guidance is needed if such pieces are to be restored. For other pieces, the following can be tried (although never on valuable pieces without practice or guidance).

Washing with hot, soapy water will often remove a surprising amount of dirt and tarnish and should always be the first step.

A light oxide can often be removed with a hard rub and repeated application of a proprietary metal (not silver) polish.

Use of a fine grade of emery paper, say 600 grade, wet and dry. A coarser grade may be tried to begin with, working up to finer grades. Dark, hard-metal items will be slow to respond to this treatment, however, and several applications may be needed.

Immersion in a solution of caustic soda will soften and remove oxide. This is an irreversible option and it is important to experiment with lengths of immersion on unwanted pieces before using seriously. Items should then be immersed in changes of clean water for several days after treatment to remove all traces of the chemical. Note – this is a dangerous chemical and should only be used with care and when wearing protective clothing. The resulting finish will be dull and it will be necessary to rub with progressively finer grades of emery paper followed by metal polish.

Some restorers also use electrolysis to remove oxide but this is an even more skilled task.

We repeat, never attempt to restore old or valuable pieces without guidance and practice on non-valuable/unwanted items!

Finally, old and valuable pieces will benefit from an application of good quality neutral wax polish to enhance appearance and protect from further oxidation.

oldmicah (author)  Kiteman3 years ago
Thanks to both of you!

The tarnish is really really tough. Soap and water got off some and silver polish got off more, but not all. (Particularly in the crevices). I'm prepping another pour and will lightly go over the plaster with a torch to ensure all of the paint is off. I'll also do a quick check with the torch to see if I can burn off the remaining residue.

After this round I'll also pick a better release agent too!

Thanks again.
caitlinsdad3 years ago
Is there any residue on your plaster mold? Soap or release agents, something in the mix of the original plaster? Is it just hidden moisture in the plaster mold? I don't know enough about pewter to say if that is oxidation, rapid cooling or reaction of impurities in the mix.
oldmicah (author)  caitlinsdad3 years ago
That is a very very interesting question. Yes there is some burning in the mold and in the sprues.

I've done a little latex molding in plaster before and I followed the same method of ensuring release... A light spray of spray paint on the clay before pouring the plaster. (not my brightest moment) Most of the paint came off with the clay, but I'm betting not all of it. (and I wasn't using lost wax method, so there wasn't a 'burning out' of the mold that might have removed it)

I hadn't seen anyone else report it, so I'm betting that's where it's coming from.

Thank you. Do you think silver polish is the way to go to get it off?
Brasso the heck out of it and spit shine your boots. I dunno. As seen on TV dip-it silver tarnish remover? Blast it off with a blowtorch?
oldmicah (author) 3 years ago
Here's the image of the discoloration.
Screen Shot 2013-06-04 at 5.37.50 PM.png