I know Jorb is considering this positively.
So, here some ideas.
2 ways to reuse :
1) Boil with ash in a cauldron.
Water mixed with ashes is a typical detergent that has been used for a long time.
If you boil bloody rags with it, you can reuse gauze hygienically.
2) Just wash in water.
This is very simple, but the quality of the gauze is greatly reduced.
And there's a greater risk of infection. Treatment with dirty gauze often worsens wounds.
Boiled gauze with ashes is also at risk of infection, but it's probably a lower probability than gauze washed in water.
All washed gauze can be used after drying at the frame. It can't be used in wet.