Prick each lime quarter with a fork.
Put the limes in a heatproof bowl, add the juice, salt, garlic and chilli powder and mix together.
Then put them in a steamer in steam for about 10 minutes, or until slices soften.
If you don't have a steamer, use a large pan with a lid and place a trivet or upside-down plate base in the plate (bottom).
Pour in enough water so it stays below the top of the trivet and cover with a lid.
Place the bowl carefully on top of the trivet or upside-down plate, cover and steam for 10 minutes, or until soft.
Transfer the limes to a bowl, cover with muslin (cheesecloth) and leave in the sun or warm place for 2 days.
If leaving outside, bring indoors at night to avoid damp air.
Heat the oil for tempering in a frying pan (skillet) over medium heat.
Add the cumin and mustard seeds and stir-fry for about 1 minute, or until they start to splutter.
Add the asafoetida and mix well.
Pour the mixture over the limes and mix well.
Cover with muslin and leave in the sun or on a windowsill for 2 more days, then remove the cloth and bottle into sterilized jars.