Brother MFC J6910DW - Manual (Page 29)

Printing
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1
Advanced Duplex Settings
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Some types of print media may need more drying time when using the duplex feature. Change
Advanced Duplex Settings if you have problems with smudged duplex prints or paper jams.
 Normal
Choose Normal to print at normal speed, using a normal amount of ink.
 Duplex 1 (Slower print speed)
Choose Duplex 1 to print at a slower speed, using a normal amount of ink.
 Duplex 2 (Slower print speed & less ink)
Choose Duplex 2 to print the same speed as using Duplex 1, but using less ink.
Note
Duplex 1 (Slower print speed) is not available for Ledger or A3 size paper.