Every body is familiar with the classic effect ashes on the palm. either from ashes or from a lipstick.

when I perform this effect I make the ash to appear on both palms.

I ask them to place any hand they want behind their back.
after the first reveal, I go further and tell them you know it happened with penetration...but the hand you kept behind your back without even contact it .... bla bla... and then I let them open the other as well.

I think sometimes less is better.

do you think that the second appear is not necessary and its better to keep it with just one?

thanks

Absolutely!

One hand is enough. Most of the time they forgot you even touched them. "Loading" the ash on both hands may cause them to remember the touch.
I use the other hand as a contrast to the chosen hand.

And I believe they are so imressed by the first appear that a second will not leave them to enjoy the effect as much

Hmmmm. I never thought about it that way. That is an awesome idea!

I think I would be more inclined to stick with just one hand. My feeling being that the less number of times you give the spectator to remember that you touched them the better.

I used a brownish red oil pastel for this one. the pastel, when the trick is done it looked like the spectator's hand was burnt but no pain!