as yet, no 'local rust' test pieces to show and tell; so here's an tile experiment with copper wire which has been followed through to completion. Single strands of copper wire were wrapped around a bisque test tile (yep, it's a bit of a pot that died on the wheel!). The tile was then dipped in clear and blue glaze and fired cone6/stoneware.
Now for the numbers/images.
Image [A] = Overview.
Graphic lines 1) 2) & 3) - show where the thin copper wire was wrapped. Line 4) shows where a single wire of much thicker copper was wrapped. Copper wire thicknesses are shown in image [E] & [F]. Yep, those are thumbnails!
Image [B], [C] & [D] = close-ups!
The types of light the photos were taken in is also recorded. I've done my utmost to get the images looking 'as is'.
Drawing attention to:
Image [D]: the resulting reflectiveness is an illusion of the photographic process and doesn't have this level of shininess in 'real viewing'. Just happened that I caught the highlight bang on max! Though this metallic 'highlight' obviously there in the photo, images from a camera are a different experience that with the human eye.
Also, with normal eye-sight my eyes cant' resolve the bubble in the glaze as shown in image. Neither can I see the texture in it's full glory as illustrated by image (and I have just had new glasses).
Copper wire wrapped around bisqued tile is never (although I'm sure someone out there can manage it!) gonna hug tight to the tile in all places. That may have effected the how the copper runs with the melting glaze.
Image [A] show that the copper runs and collects through the melt.
Image [C] shows the copper 'really going for it!'
For extra points, the exceptionally observant of you may suss that the test tile has been slipped before bisque firing. The top third of the bisque was fired with added white slip, the bottom third, black – which fired up blue! The middle has no slip added and is just clay body, plain and simple.
I think that covers it!