While there are no guarantees, I noticed something the other day that I can't wait to try.
When using herring for cutplugs, I buy the frozen variety, brine them with a bit of cream and a few drops of Mothers Bluing. Really works to keep them firm and shiny, but as I observed, not as shiny as a fresh herring. This came to me while catching herring off the rocks a week or two ago, I noticed that I could see the herring on my hooks flashing 50 -70 ft away as I brought them into shore. Last weekend while fishing in Barkley Sound, I was using my shiniest frozen herring and even on a bright day, the bait wasn't anywhere near as flashy as the fresh one. My observation and tip is that when ever possible, use fresh bait. And if not keep your bait as shiny and fresh looking as you can.

Good luck and tight lines.

One thing we did to our herring while cutplugging was to use powdered milk.. It works like a hot damn to keep the little buggers shining deep down. Premix it with your course salt and ice cubes. You don't want it to get warm.. Your bait will stay firm as long as the water is kept cool. Don't use to much or it will soften your bait beyond usefulness.-dirty

yes the powdered milk is tops and brine and brite will get em shiny.you will never achieve fresh quality but you can get close.Ss out

What sort of proportions? --Powdered milk to salt to water? How long do you soak them?

I use about a cup of milk powder in a gallon of water,salt of course.4cups,2 tbs bait brite.does about 4 doz or more.soak for few hours or longer.as long as you wish but use ice and keep in fridge.must keep them chilled.Ss out.