Need of purple color, i bought Amaco velvet underglaze 12 packet, so I can test many underglaze with V380 violet, my target.
Result: V380 is pretty useful and stable purple, though it is a bit too light for my preference.
Below are other results
V381 amethyst, not my favorite at all, became too dark over iron rich clay, might work for white clay
V375 not useful at all, color vanished in cone 6 firing.
V385 cinnamon, too shiny
V386 too shiny blue
V383 really close to 6026 red, bit too shiny in cone 6
V373 medium brown, good cardboard color, useful for cardboard replica
V384 good orange and stable in its surface, I like it
V374 Nice light pink with a bit yellow shade, become shiny in thick area, might work on cone 5
V376 Hunter green, a bit blue green, surface is reliable, like it.
V372 Mint green, lighter version vermuda green, good for mint flavor.