Recently, I've been studying my early Australian decimals pretty intensively, largely because many of them look simply fantastic under UV. With the QEII defins, I find myself perplexed by the whimsical shapes (squiggles and chequerboard patterns) that appear as lighter and darker areas within the fine mesh background. Here are two examples:


Does anybody know how these 'squiggles' and 'patterns' are created? And if they're intentional or not? And if there is something similar on stamps from other countries?