Wash a small amount of Swiss Chard at a time, to ensure you are being thorough. Wash in a sink or tub of water, then drain and rinse until rinse water runs clear of any dirt or grit.
Trim off and discard tough ribs and stems.
Put about ½ kg (1 lb) of Swiss Chard at a time in a cheesecloth bag, or a basket, and steam until well wilted -- about 3 to 5 minutes.
Pack loosely into ½ litre (US pint) jars or 1 litre (US quart) jars.
Leave 3 cm (1 inch) headspace.
Top up with clean boiling water (such as from a kettle, for instance), maintaining headspace.
Debubble, adjust headspace.
Wipe jar rims.
Put lids on.
Processing pressure: 10 lbs (69 kPa) weighted gauge, 11 lbs (76 kpa) dial gauge (adjust pressure for your altitude when over 300 metres / 1000 feet)
Processing time: half-litre (US pint) jars for 70 minutes OR 1 litre (US quart) jars for 90 minutes.