To make a spray tan finishing powder, you will need a few key ingredients that will help set and enhance the appearance of your spray tan. Here is a simple recipe to create your own spray tan finishing powder:

Ingredients:
- 2 tablespoons of cornstarch
- 2 tablespoons of arrowroot powder
- 1 tablespoon of finely ground cocoa powder (optional, for a bronzing effect)
- 1 teaspoon of finely ground mica powder (optional, for a subtle shimmer)
- 5-10 drops of your preferred essential oil (optional, for fragrance)

Instructions:
1. In a small bowl, combine the cornstarch, arrowroot powder, cocoa powder, and mica powder (if using). Mix well to ensure that all the ingredients are evenly distributed.

2. If you want to add fragrance to your finishing powder, add a few drops of your preferred essential oil to the mixture. Stir thoroughly to incorporate the fragrance.

3. Transfer the mixture into a clean, airtight container. A small jar or a powder sifter container would work well for this purpose.

4. To use the spray tan finishing powder, simply apply a light dusting of the powder onto your skin after your spray tan has fully dried. Use a powder brush or a powder puff to gently apply the powder in a circular motion, focusing on areas that tend to get oily or shiny.

5. The finishing powder will help to set your spray tan, reduce any stickiness or tackiness, and provide a smooth, matte finish. The optional cocoa powder will add a subtle bronzing effect, while the mica powder will give a delicate shimmer to your skin.

Note: It's important to conduct a patch test before applying the finishing powder to your entire body, especially if you have sensitive skin or any known allergies to the ingredients.