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Japanese technique Shotai Shippo for plique a jour enamel

Hello All,
I recently found a photo of an amazing vase made in Shotai Shippo technique. It is a type of plique a jour enamel, but it’s done slightly different, than traditional plique a jour that I’ve heard about. The cooper plate is covered with clear flux, burned and then gold or silver wires are glued to the surface and filled with transparent enamel - exact same as traditional cloisonne.
But after the process is complete - copper is dissolved in the acid bath and there will be only glass. Looks very beautiful, as wires are very thin and it creates an additional lightness and transparency.
So I was wondering:

  1. If I need to use counter enamel - how I would remove it?
  2. What type of acid would be appropriate to remove copper and how to protect the face of the piece from acid? And if I protect the front - would the back side of enamel impacted by acid when copper starts to disappear?
    I wouldn’t risk to do a vase, but small jewelry piece in this technique would be nice. I and kind of excited that I don’t have to pierce hundreds of cells in the sheet of metal (night mare). In general I understand cloisonne technique and this method would be much easier to implement if I understand copper removing part.

Can you scan and forward to the group the photo you found?
Jo

Note that ferric chloride will etch copper but not silver…(not ferric nitrate which will react with silver)
it is available from various sources - electronics shops usually carry it for etching copper circuit boards.
I used to make ferric chloride industrially and it is slightly acidic and relatively benign.
Regardless, read the SDS with the material and wear your PPE.
Ferric chloride will stain skin and clothing and dry out skin. It is a strong irritant, and potentially damaging, to eyes, and poisonous, as would be an overdose of iron pills. Most commonly used to treat and clarify municipal drinking water.
However, for our purposes it reacts strongly with specific metals like copper and steel. But not so much with silver. Not sure of sterling silver vs fine silver
Doesn’t this technique require soldering the fine silver pieces together? One technique I know of calls for using a eutectic solder. But the alloys in solders is another potential issue with reactivity to ferric chloride…Eutectics being the lowest.
As far as reaction with the glass,not generally, but test pieces for specific enamels would be my advice. Some enamels do react in hot pickle…
WRT protecting to front surface maybe not necessary but I’ve been suspending my etchings with a long piece of ‘duck’ or packing tape to the sides of a low glass container.
Hope this helps

Images can be seeing in this website: https://galleryjapan.com/locale/en_US/technique/otherworks/70104/

  1. You don’t counter enamel, this defeats the technique, (and you don’t “burn” enamel - you fire it.)
  2. You etch off the copper with nitric acid or Ferric nitrate. You could also electro-strip.
  3. You can protect the front with wax or etch resists.
  4. Some enamels, especially leaded ones, will get dulled by the acid. Also the enamel on the back will have taken the micro contours of the copper sheet. After a thorough clean you “flash fire.” (ie into a very hot kiln and out again as soon as the enamel goes glossy.)

Based on the brief description of the shotai shippo technique, that I found - wires are not soldered. They are applied like in traditional cloisonne and sitting on the clear enamel base. In fact shotai shippo is the same as cloisonne, but backing material is later removed. I found some references that nitric acid was used for removing copper.
The question re. counter enamel. In vases - counter enamel may be not necessary, as it is 3D form, but if I would make a flat form - not sure how to do it without counter enamel. If I remove it later - will it impact the piece?

You are right, “fire” - sorry for that.

So nitric acid will react with silver (and copper).

"Silver react with nitric acid

Ag + 2HNO3 → AgNO3 + NO2 + H2O"

Source: https://chemiday.com/en/reaction/3-1-0-1559

“This method of etching uses a ferric nitrate solution which also contains nitric acid. This “etchant” is not a pure acid, but etches fine silver and sterling silver (ferric chloride will not etch silver). CAUTION: Although etchant is not a pure acid, it is a “corrosive poison”.”
Note also that nitric acid is significantly more hazardous than ferric chloride (which is messy but doesn’t fume or burn skin).

Don’t know if you’ve done Plique a jour but these YouTube’s helped me get started

Plique-a-jour Part 1

The Japanese method looks really difficult… and prone to failure

Hoping this useful.

Good luck