An old technique from my watercolour days that I still love to use for backgrounds.
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Paint you heart coaster with a chosen background colour. I have used Americana Baby pink here and then sponged over lightly with warm white

Next I diluted some American Royal Fuchsia with 40% water. You want a deeper tone than your base colour. This was then quickly painted over my background using a mop brush and sea salt was sprinkled into the wet paint. Once dry remove the salt with a stiff brush and it is ready for stamping!

If using as a coaster I would recommend sealing with Americana Traditions Satin Varnish. This is a quick drying resin-based polyurethane varnish which provides the hardest acrylic finish available for indoor and outdoor surfaces. When four coats are applied it also becomes alcohol resistant.
Here is a salt coaster with a gloss finish.
CLICK ON PICTURES FOR LARGER VIEW
Paint you heart coaster with a chosen background colour. I have used Americana Baby pink here and then sponged over lightly with warm white
Next I diluted some American Royal Fuchsia with 40% water. You want a deeper tone than your base colour. This was then quickly painted over my background using a mop brush and sea salt was sprinkled into the wet paint. Once dry remove the salt with a stiff brush and it is ready for stamping!
If using as a coaster I would recommend sealing with Americana Traditions Satin Varnish. This is a quick drying resin-based polyurethane varnish which provides the hardest acrylic finish available for indoor and outdoor surfaces. When four coats are applied it also becomes alcohol resistant.
Here is a salt coaster with a gloss finish.