Question about opaque white ink

Since starting to print with my Vandercook, I had used only transparent white in my color mixes, but after reading here in the archives that some people recommended using opaque white rather than transparent when mixing pastel colors, I used it for several projects and have been very happy with the results. I’m wondering if it is possible to also get darker colors using the opaque white or is it appropriate for lighter shades only? (I am using rubber based inks).

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Back in the day, an ink company friend, in Wallingford, Conn. (Murray Bleau, Marathon Ink Co., hi Murray) told me, the opaque inks he was making for me had a maximum of 20% opaque white in them. He said he used various means to do that. Titanium oxide as I understand it, is the pigment (very heavy).
Putting an excess amount of it in a mix definitely pulls the mix in the direction of blue, so sometimes adding is limited.
Also, when mixing in the shop, on the fly, utilizing a PMS book, I always started about 2 steps (swatches) previous from the swatch color desired for letterpress, as a thicker film is usually laid on the paper and prints darker than the swatch in the swatch book. Lessening the amount of black in the formula also helps sometimes if, the paper the job is to be printed on is an off white or darker, adjust as needed.
One of the nice things about adding the opaque white in a letterpress mix was, the white stocked, was of a high tack and would give the runny offset inks a bit of body so it would print crisper.
Two or three hits of opaque white on dark stock seems to print a better looking silver solid than silver does, on some colors, I always thought.