The Shadowlands pre-expansion Patch 9.0.1 is going live on October 13th in NA (October 14th in EU)! There are a lot of changes to classes and basically everything, but there are very few profession changes. I will only focus on the new Relic of the Past optional reagents in this post, but you can read through all the new changes on mmo-champion.
Table of Contents
- What are these 'Relic of the Past' reagents?
- Who can craft Relics of the Past?
- Where to learn Relic of the Past recipes?
- Where to get Penumbra Thread, Luminous Flux, and Curing Salt?
What are these 'Relic of the Past' reagents?
New optional reagents that you can use to increase or decrease a crafted item's item level and level requirement.
Who can craft Relics of the Past?
Tailors, Leatherworkers, and Blacksmiths can create 5 different relics:
Relic of the Past I - Set the Item Level to 19 and the Required Level to 14
Relic of the Past II - Set the Item Level to 28 and the Required Level to 23.
Relic of the Past III - Set the Item Level to 39 and the Required Level to 32.
Relic of the Past IV - Set the Item Level to 48 and the Required Level to 41.
Relic of the Past V - Set the Item Level to 54 and the Required Level to 47.
All 5 of these can be crafted with 24 different materials. (different materials from each expansion for each profession).
So, for example, you can craft Relic of the Past I with 8 different cloths. The 8 recipes below all make the same item, the different versions were added so it won't matter where you level with your character, you can always make useful gear by using these.
- Relic of the Past I - 5 x
Linen Cloth, 1 x 
Penumbra Thread - Relic of the Past I - 5 x
Tidespray Linen, 1 x Penumbra Thread - Relic of the Past I - 5 x
Sumptuous Fur, 1 x Penumbra Thread - Relic of the Past I - 5 x
Netherweave Cloth, 1 x Penumbra Thread - Relic of the Past I - 5 x
Shal'dorei Silk, 1 x Penumbra Thread - Relic of the Past I - 5 x
Windwool Cloth, 1 x Penumbra Thread - Relic of the Past I - 5 x
Embersilk Cloth, 1 x Penumbra Thread
Where to learn Relic of the Past recipes?
You can learn the recipes from each expansion's profession trainer. (you will automatically learn the new Legion and Draenor Recipes).
You can find the trainer's location in each of my profession leveling guides if you are having trouble finding them. You can also just walk up to a guard in major cities then ask where the profession trainer is. Asking the guard will place a red marker on your map at the trainer's location.
Where to get Penumbra Thread, Luminous Flux, and Curing Salt?
These items are sold by Blacksmithing, Tailoring, and Leatherworking supply vendors in main cities. I haven't checked every single vendor, so I don't know every NPC who sells them, but I can confirm that you can buy them from the vendor near your trainer in Orgrimmar, Stormwind, Dazar'alor, and Boralus.
Links to NPCs in Orgrimmar and Stormwind:
Luminous Flux is sold by 
Punra in Orgrimmar and by 
Kaita Deepforge in Stormwind.- Penumbra Thread is sold by Borya in Orgrimmar and by Alexandra Bolero in Stormwind.
Curing Salt is sold by Tamar in Orgrimmar and by Jillian Tanner in Stormwind.