Making your own washing soda is easy. However, for those who can buy them cheaply, then there would be no need to make it yourself.
Washing soda is a degreasing agent which can be used in dish detergent and laundry detergent. Making it requires only one ingredient: baking soda.
Here are the steps to make washing soda:
1. Preheat the oven to 390-400 degrees Fahrenheit (200 degrees Celsius)
2. Evenly pour baking soda into a pan or tray that can be baked in an oven.
3. Bake for 1 hour.
4. Let cool and carefully pour into a container for future use.
Warning: Washing soda is somewhat toxic. Do not ingest. And keep out of the reach of children.
Here is a link to an article about the subject: