These are real eggs that were hard-boiled with strips of colourful silk ties wrapped around them. Over the strips one ties white cotton material. I used some elastics to hold the silk in place as well as the cotton. Linen would work, too. But don't use something you don't mind being stained.
The key to this little exercise are the three table spoons of white vinegar added to the water. The acid leeches the colour from the tie and imprints it on the porous egg shell.
The eggs must be boiled for at least 20 minutes. I find 30 better, and then cooled to room temperature. I plunked one egg into ice water but this does not seem the best thing to do.
One thing I tried, in order to get better colour was I used white glue and glued strips to the egg. This kept the two surfaces in better connection and meant not so many uncoloured spots. The glue, of course, melts in the water and it is easy to unwrap the egg.
I must confess that I added the yellow and turquoise as the ties I used were monochromatic.
This would be an excellent Easter endeavour to do with older children and husbands.