This is a waxing tool called a “kistka.” It has a metal cup with a tiny hole at the bottom.
Fill the kistka with beeswax, and heat it over a candle flame to melt the wax.
Use the kistka to draw lines of melted wax on your egg.
The wax will keep dye off the egg, so wherever you put wax at this stage will remain white.
Dip the egg into the first color of dye – in this case yellow.
Notice that the waxed lines have been protected from the yellow dye.
Now, draw wax lines in all the places that should remain yellow.
Continue in this way, adding layers of wax and different colors, until the design is complete.