Master writ chances are completely character-based.

While they initially stated they were "achievement-based", that was incorrect, as they are using the Lore Library to track whether a character knows specific things.

From what I've tested/reported from ZoS.

Blacksmithing/Woodworking/Clothing - Researched traits (only need 1 of each of the 9 types, so you don't need to research all on everything) and Motif knowledge (Tracked by the lore library; heavily weighted to the first few that you learn)

Jewelry - Researched Traits

Provisioning - Purple and Gold recipes known

Enchanting - Runes translated

Alchemy - Properties translated (all 4 needed)

Much of this is included in the spreadsheet linked in my signature on the first tab about what increases the drop rate.

One_ofMany wrote: »

So only 1ea of all 9 in the Blacksmithing/Woodworking/Clothing? So I could do 9 separate weap/armor with one diff on each one and that is all need? Does learning more increase or is it capped?
Thank you!!

The original statement was for the achievement, and you only need to research each trait once for the associated achievements. So I'm going off of that. The trait knowledge for BS/WW/Cloth is on the order of a few percentage points increase in the chance. Motifs can give you a larger boost.

I started researching traits long before writs even existed, so I don't have data to confirm or deny the original statement from ZoS on what affects the drop rate (with regards to trait knowledge).