Canning method
Combine the vinegar, sugar, celery seed, allspice, and mustard seed in a large pot. Bring to a boil and keep hot.
Pack the kelp chunks into hot pint jars, leaving 1/2-inch headspace. Pour hot brine over the kelp, maintaining 1/2-inch headspace.
Remove air bubbles, readjust headspace if needed, wipe the jar rims, and apply prepared lids and rings.
Processing: Process pint or smaller jars for 16 minutes in a boiling-water canner. Yield: about 4 pints.