Let me clarify the three Piezography shade 1/black inks.
Originally, we had Neutral shade 1 for non-gloss printing, and Selenium shade 1 for gloss printing. A few years later, we came out with Piezography Warm-Neutral ink, including a new glossy compatible black- WN#1 (AKA “Opaque Black”).
WN#1/Opaque Black is slightly darker and slightly glossier than SEL#1, but many people who have been using SEL#1 wish to continue using it, and the Piezography Digital Negative system was developed with this black.
In the lower levels, WN#1 is slightly warm and SEL#1 is slightly cool- but at the level where they are printed, both are deep black and I would say the slight warmth/coolness is not noticeable.
All our Piezography printers (we have five 7880/9880 model printers, each set up with a different Piezography ink tone) are using the WN#1/Opaque Black for glossy printing, and I personally prefer to use WN#1 for all glossy printing, except when printing on film I use the SEL#1.
I hope this helps. Please let me know if you have further questions or if there’s anything else I can help you with.
Best regards and happy printing~ Dana