The slow blink is the most misunderstood gesture in the repertoire. To the untrained eye it is a person falling asleep. To the trained, it is a treaty. The correct form is a half closing of the lids, a pause of two seconds, and then the full close, delivered with a faint air of having more important things to do.
Beginners over blink. This conveys desperation. Experts under blink, which conveys an intriguing malice. I recommend practising before a mirror, or better, before a bowl of cold chicken, a more honest audience. After six weeks of such training I successfully slow blinked at a postman and he gave me a nod I have been thinking about since. It might have been a tic. I choose to believe in treaties.