Add the bicarbonate of soda, citric acid, epsom salts, and cornflour to a medium bowl.
Stir with the whisk until the dry ingredients are completely combined.
Add the calendula petals and gently stir through.
Pour the sweet almond oil, water, and essential oils into a small jar, and secure the lid.
Shake the jar to combine the liquid ingredients.
Very slowly, whisk the liquid mixture into the dry mixture. Whisk the entire time, so as not to activate the fizzing properties in the bath bombs.
Scoop the mixture into each half of the bath bomb mould, then press together, and give a quick twist.
Allow the bath bombs to set for at least 8 hours.
Remove from the moulds.
Store in an airtight container until ready for use. These bath bombs should last for 6 months, if stored in an airtight, moisture-free container.
Tip - in humid climates, you may need to decrease the amount of liquid you use, so slowly pour some in while whisking, then ¼ of the way through, check the texture to see if you can form it in your hand. You want it to be able to form, but not be too wet.