1. Prepare the silver piece.
Depletion gilding must be applied if it's made of sterling silver, because this patina is only available for silver. Without it, you wouldn't get good results.
2. In this video, I polished it with a wire brush to get a shiny surface.
3. Then I polished it with baking soda to degrease it.
Degreasing is very important in any patination process.
4. Prepare the solution.
You need 100ml vinegar, 6g copper sulfate, and 6g salt. You might find copper sulfate at aquarium stores, garden suppliers, and hardware shops. It is available as a fungicide, root killer, algaecide, and herbicide. Make sure it's pure copper sulfate (pentahydrate) without any additives. Mix them well.
5. Dip the piece in the solution.
Sometimes it darkens within a few minutes even at room temperature, but I needed to warm it up in this video. I use a mug warmer in such cases. The temperature is 50°C (approximately 120°F) and the time is around 5-10 minutes. Then wash it with running water. The patina is a brownish black color, or it might be a dull dark brown. I always apply Renaissance Wax as a finish. Like all other patinas, this patina will wear off. I don't recommend applying it to rings.
6. About disposal.
You can reuse this solution again and again. But eventually you'll need a fresh solution. This solution contains a lot of copper ions, and in many cities it's prohibited to dump it down the drain as is. You need to remove the copper ions from the solution before disposal. To do this, add some aluminum foil to it. Aluminum ionizes more easily than copper, so the copper ions are reduced back to metallic copper and sink to the bottom of the container. Then dispose of only the liquid solution and wipe out the copper sediment. To discard the copper, check your city's regulations—it's just metallic copper.
You see example pieces in my shop.
https://www.kaznesq.com/product/sale-fan-pendant-japanese-patina-pearls-and-coral
https://www.kaznesq.com/product/pearl-and-silver-pendant-japanese-patina-and-keum-boo-inspired-japanese-partition