What type of design project is most suitable for showcasing the beauty of Celtic letters?

The most suitable design project for showcasing the beauty of Celtic letters is a greeting card. Greeting cards often provide a personal and intimate way to express sentiments, making them an ideal canvas for decorative and elaborate lettering styles such as Celtic calligraphy. The intricate patterns and unique letter forms characteristic of Celtic scripts can enhance the emotional appeal of a greeting card, drawing attention to the message while also serving as a piece of art in itself.

In the context of the other options, a technical manual typically requires straightforward, clear typography that prioritizes readability and function over artistic design, which would not allow the ornate features of Celtic letters to shine. A historical document, while it may incorporate calligraphy, often needs to adhere to specific formats and conventions, limiting the potential for decorative elements. An artistic mural could be a viable option for displaying Celtic lettering; however, it generally focuses on large-scale visual impact and may involve more contemporary or thematic representation instead of the detailed intricacies of Celtic letters.