i spent a good amount of time this weekend adding Reprolabels to my CW Devastator. as i was adding the various stickers, i was struck by just how many sculpted details there are all over. i've used Gundam markers and others for enhancing panels lines before but what about this: Amazon.com: TAMIYA Panel Line Accent Color 3-colors(Black,Brown,Gray) Set [Japan Import]: Toys & Games TAMIYA Panel Line Accent Color has anybody used these on Transformers or Gundams before? it seems deceptively easy to use and the "may harm plastic" warning is scaring me off a bit.
As long as you put down a gloss coat before using the enamels, you should be safe. The guy at my local shop recommends this Citadel Nuln Oil, tho if you've got a hobby shop near you it should be MUCH cheaper (like $3-6 instead of the $20 on Amazon).
I do half part darker green and half part Zippo lighter fluid. Use a fine brush and dab in the lines. You'll see alot of it fill itself. 10 minutes to dry then gently Q-tip the excess with thinner. After all is done and stickers applied (apply reprolabels/stickers before panel line) I like to apply a nice flat coat. Ez peezy lemon squeezy
I use vallejo washes and it works well. However the best is one I made using a tiny bit of dishwashing detergent, distilled water and black paint. It doesnt stick to anything on top and only sticks to edges. I didn't record how much I mixed :\ but you can try that.
I did my devy with simple acrylic. I just mixed up a slightly darker green, watered it down, and put it into thee panel lines. Nothing too fancy and a lot subtler than black or dark green but it was enough to make a huge improvement. Before doing this, Devy was an almost radioactive green; now he looks much more accurate but without thee crazy dark panel lines I've seen so many people use.
White Spirits also make for awesome thinners for panel lining. AK Interactive makes some awesome weathering and lining paints, and they're relatively cheap on Amazon. Whatever you do, do NOT use straight black. Sometimes, black lines on colored plastic look horrible. I will always recommend either using a shade of the base color or a complimentary color.
THIS use either a tint color [tamiya smoke] or a darker version of the color you're using. use black only on dark colors like dark blue, purple, red, brown. NEVER line white with black. use a ghost gray or light grays.