I have been experimenting with underglaze decals. The best I have found are from Sanbao ( chinaclayart.com ). You can get a 6x8 sheet for $2.25. Application is simple since you do not have to put additional underglaze on the sheet. Simply place the piece on either leather hard or bisque ware, use a paintbrush or sponge to apply water, and pull the paper off.
I am firing to cone 6 with a Chun Celedon glaze on top. The “dots” are hand applied with designer liner.