Sold a tanzanite CZ and always have to give a color change run down

I do sell some larger CZ’s on eBay and Etsy and from time to time they are being purchased by metal clay artists.

Made me think of throwing the information up here quickly for those of you who have avoided using some of them because of this issue.

I discovered this a couple years ago quite by accident.  I was taking a class from Hadar in mixed metals and had a supply of my aqua CZs which had turned amber (beautiful by the way) and thought they would look so sexy in copper/bronze mixed metal pieces.  Hadar thought so too.  So I set them into a pair of earrings.

Well, after firing in carbon they returned to aqua!  Not attractive in bronze/copper but a big “whew” for silver.

So I went home and fired all the different CZs that had changed colors again in carbon.  I discovered this:  CZs that change color in open air firing will return to their original color if refired in carbon. 

Aqua full ramp 1000F 5 min   amber back to aqua  
Emerald full ramp 1000F 5 min  sienna back to emerald
Tanzanite full ramp 1600  40 min  dark garnet back to tanz
  the coolest thing about the tanzanite is that they change slowly     
and if you time it correctly you can get a really cool smoky tanz grey color.  Something very different.  Looks awesome with silver.  My best estimate for that one is full ramp 1200F 15 min.
    All of these need to come to room temp in the carbon or they change back to their “alter”

I haven’t had other colors change on me except years ago when I did my RIO Cert class an opaque black CZ turned into transparent salmon pink.  Very weird and haven’t been able to do anything with that one.

Now, if I want to gypsy set stones I know will change in fine silver open air firing, I simply refire the piece in carbon after it’s finished and do the regular polishing, los or whatever else I choose.
FYI if you plan to enamel, it will change again.  I’m going to try refiring an enamelled piece, under a mesh tent, in carbon (at the lower temperature) to see if the enamel will become angry or if it will accommodate the stone.
  Of course they shouldn’t change in sterling because of the carbon. 

In any case, if you do like the color change it won’t happen in carbon.  Sorry.  You have to open air fire it.  Now, I can definitely see trying to change the aqua ones to amber, set in copper, with enamel firing. Time for more experimentation.      

I’ll let you know what happens.

About Donna Lewis

I'm still fascinated by the process that metal clay goes through from its initial form to finished work. A variety of techniques: both unique to metal clay, and standard in traditional goldsmithing; are combined to create some of the most individual signatures in art jewelry today. Absolutely thrilled to see what comes next!


Sold a tanzanite CZ and always have to give a color change run down — 3 Comments

  1. Donna, this is a really helpful tip. Quite some time ago I bought a lot of emerald CZ’s. Although I like the brownish color after burning in the open, I do prefer the striking green. And now I am able to re-create the color. Thank you!

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