To commemorate 35th Anniversary of the Constitutional court, Spain Post has issued a single stamp Miniature sheet on 23rd July 2015. The uniqueness of this Miniature sheet is the cold foil printing technique. I have many hot foil stamps, but this is first one for cold foil. (It seems recently Liechtenstein issued three cold foil stamps under 'Princely treasure' theme - I don't have them yet).
Brief look at Cold foil and Hot foil techniques:
In cold foil technique, gum is applied to the area where foil has to be placed and then the foil is pressed with the help of UV light. Then colour is applied on the paper and foil through ordinary printing. Since the technique is very simple, the cost is less. Cold foil technique is preferred when large area needs foiling or when precision is needed.
Whereas in Hot foil technique the design block (mould-like) has to be made and the foil is pressed on the paper with the help of this block. The colour is restricted to the colour of the foils available. Embossing can be done along with foil pressing. It is not recommended for tiny area. The block making and special printing make this technique costly.