Thanks for asking these questions Greywash - Drops or pre-mixed?
I actually don't tattoo with grey wash very often. I used to a lot & really enjoy the process, but I fell in love with the bold look of opaque greys.
I still use grey wash on smaller tattoos when it seems more suitable. I use a drop system using regular distilled water. I use to have lots of different mixes in caps, but over time have gone to using straight black, 50%, 20% & 10%.
Opaque greys -
Opaque greys are a very different process, because you are selecting the right value straight from the bottle & matching to the reference. I think of opaques as advanced black & grey because there is less room to alter things, by building layers gently. You have to be way more intentional where you are putting values straight away.
Tattooing darker to heal better -
I do like to adjust contrast & often increase colour saturation of my reference photos, but i always do that before I start tattooing. I like to make those decision before printing my reference. Then I match the tattoo very closely to the printed copy. I like to have that on glossy photo paper next to where i'm tattooing.
Tattoo Process -
I do work dark to light, but more in sections (maybe a 3-4" areas) often completing that section, then moving to the next. With opaques I put the very lightest greys in once most of the area is finished.
Going a little darker when you tattoo grey wash can be a good idea, but it helps to see how your tattoos heal on skin. You can always darken a little on a second pass, but you can't lighten a tattoo afterwards!
Greywash does often lighten because its transparent & the top layers will heal leaving a little less Ink in the layers.
Thanks for asking these questions Karl. And if you need any of this clarified just let me know.
I'll share more info on my opaque setup later!