You need this:
- self-adhesive template (eg from HSI, about 3.40 euros)
- mirror
- thrush
- clothes peg
- Satinierfarbe (eg Satine varnish from Viva Decor; craft shop)
It's that easy:
1. Stick the template on the clean, grease-free mirror.
2. Dab satin with the sponge.
3. After a short drying time, remove the stencil.
Tip: For better handling, clamp the sponge in a clothespin.