When choosing a pattern for stained glasses, an important thing for consideration is the purpose of the glass. For instance, if the glass is going to be used in a window, it has to be a pattern that is appropriate to the room the glass will be placed in. On a leadlight panel for a door, the patterns should not be too detailed as this often increases the weight of the glass, which is not ideal for a door panel.
Another factor that needs to be taken into account is the light. If the stained glasses are going to be used in leadlight windows, then it is likely that they will be backlit with natural light. This means that these windows could accommodate brighter colours. However, if the glass is going to be merely as a piece of art hung on the wall, then the colours used in the pattern will have to be used carefully, so as not to make the entire painted glass look dark.
Working with a professional will enable you to pick the pattern giving necessary consideration to all the factors. The glass professional will have a portfolio of patterns that can be selected from, or you can create your own pattern. An interesting way of creating a pattern is to use a photograph to create a stained piece of glass. This can be done digitally and the glass professional can then select a suitable contrast of colours based on the decided factors.