Doubling Cube
Artifact
, 
: Double the amount of each type of unspent mana you have.
The cube's surface is pockmarked with jagged runes that seem to shift when unobserved.
Mark Tedin
Tenth Edition (10E)
• #321Rulings
Doubling Cube's ability is a mana ability.
(wotc • 2004-12-01)
Any restrictions on the unspent mana aren't copied. For example, if you have {C}{W}{W}{B} with no restrictions on it and {U}{U}{U} that can be used only to cast artifact spells, you'll end up with {C}{C}{W}{W}{W}{W}{B}{B}, {U}{U}{U} that can be used only to cast artifact spells, and {U}{U}{U} that can be used for anything.
(wotc • 2004-12-01)
The "type" of mana is its color, or lack thereof (if the mana is colorless).
(wotc • 2004-12-01)
Rulings
Doubling Cube's ability is a mana ability.
(wotc • 2004-12-01)
Any restrictions on the unspent mana aren't copied. For example, if you have {C}{W}{W}{B} with no restrictions on it and {U}{U}{U} that can be used only to cast artifact spells, you'll end up with {C}{C}{W}{W}{W}{W}{B}{B}, {U}{U}{U} that can be used only to cast artifact spells, and {U}{U}{U} that can be used for anything.
(wotc • 2004-12-01)
The "type" of mana is its color, or lack thereof (if the mana is colorless).
(wotc • 2004-12-01)