Digital BW, The Print

I am planing to mix multiple shades of b&w inks from Photo Black (PK) 
for printing on glossy paper. I have a few questions:

Is photo black a result of mixed color inks? What is a good ink base 
formula for mixing with photo black - I wish there is a version of 
colorless Windex :).

What is a good ratio of ink base vs PK ink? For example,
    3 shades: 100% PK, 50% PK, 12.5% PK
    4 shades: 100% PK, 50% PK, 25% PK, 12.5% PK
    6 shades: 100%PK, 75% PK, 50% PK, 25% PK, 12.5% PK, 6.25% PK
    8 shades: Any benefits for that many shades?

Thanks,
- Philip