I spent a few days making the Masterwork Staff (mostly from) scratch. I tried to deduce the process myself, though there was some unsolicited help from the FC. I've outlined the steps, not necessarily in the order I did them.
You can find a full guide with item requirements on the RSWiki.
1. Complete the "Crafting Your Own Rune" achievement.
2. Obtain the Abyssal Runic Synapse from Runecrafting via The Abyss.
3. Create 3 volatile bricks:
3a. Chip 3000 pure essence into fragments
3b. Use the 3000 fragments with 3000 of each rune at any altar.
4. Smith the Masterwork Focus Bracket
-2 gold bars
-1 glorious bar
5. Smith the Grounded Masterwork Staff Base
-2 gold bars
-1 volatile rune brick
-4 crystalline essence
6. Break down 2 of each into their components at the Dragonkin Forge:
-Cywir wand/orb
-Crystal staff
-Seismic wand/orb
7. Craft the Masterwork Runic Conduit out of Melodic essence and a volatile brick and Imbue it. (rune altar)
8. Craft the Masterwork Focus Housing out of the Conduit and Abyssal Synapse (rune altar)
9. Create a Rune Imbued Diamond out of a diamond and Binding essence.
10. Imbue the Runic Diamond at the Elemental, then Catalytic altars.
11. Smooth out the Catalyzed Diamond and combine it with a volatile brick.
12. Use the Unhoused Masterwork Focus with the Focus Housing to create the Housed Masterwork Focus (rune altar)
13. Craft 20 eternal magic staves (2 eternal logs each) and use them on a rune altar.
14. Get undead dragon leather, dye it brown, and combine with the Masterwork Staff Grips.
15. Combine the Masterwork Grips with the Grounded Base to complete the Staff Handle (rune altar
16. Last, combine the Masterwork Staff Base with the Masterwork Staff Grip at a rune altar.
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Credits for the music, all tracks included owned by Jagex.
"Autumn Voyage" (Originally composed by Ian Taylor, new arrangement by James Hannigan)
"We Are the Fairies" (Composed by Adam Bond)
"Scape Cave" (Composed by Ian Taylor, new arrangement by Adam Bond)
"Rune Essence" (Originally composed by Ian Taylor, new arrangement by Adam Bond)
"Wander" (Composed by Ian Taylor)