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If you're like me, you mess up A LOT while inking, and you want to use the right correction material for the job. Many white inks are just not opaque enough to be up for the challenge. When making small corrections, I use the white gel-pen mentioned above, and have found it to be satisfactory, with only a few occasions for additional touch ups. It is the best white gel pen I have used so far, but if you know of a better product, please let me know.
When applying these inks, I used the same brush I use for making corrections. Some of these inks are intended to be used in an actual pen, as I do not use them for such, I did not test them for those qualities. The main concerns I had were opacity, drying time, and finish. Each of these swatches have only received one coat.
The Dr Ph Martin's Bleed Proof White has consistently show to be the most opaque of the correctional inks I own, but it dries very slowly and dries shiny. It is hard to make marks over this ink, and the best tool to go over them is a brush or brushpen. This ink still requires another application to sufficiently cover marks.
The Japanese ink that I purchased off Jetpens appears to be fairly opaque in this swatch, but in actual application, it is not opaque enough to cover lines made. I often have to go over it two or three times. It also dries shiny and takes awhile to dry.
The Koh-i-noor white ink is intended to be used with a pen or nib, and is very thin. I do not recommend it for correctional use.
The Daler Rowney Gouache is the most opaque in actual application. It takes a little while to dry, works best when used with a little bit of water, and is hard to go over, but it dries faster than the Bleed Proof White and is much less shiny. If you are VERY careful, you can go over it with tech pen. It is easy to go over it with brush. The only real problem with the gouache is that it cakes with repeated application.
Hey! Jetpens, my favorite source online for comic supplies, has an excellent comparison of their various white gel pens. Looks like I'm going to need to convert.