@Thedoc_tv Unlined copperware is banned because the copper can leach into acidic food and drinks at high temperatures. Tsuiki copperware is lined with either tin or silver. Which liner is used depends on the nature of the item. Mass-production items for sale in the shop or art competition items are normally lined with tin. Custom ware intended for actual use is often lined with silver.
Copper reacts to acid thats why non reactive metals are used to line the cooking surface. In fact having nearly everything copper in a restaurant kitchen was a status symbol because copper is easy to get dirty and show minor corrosion so a pristine copper kitchen showed how often it was cleaned and maintained.