Context : Open clusters are a useful tool when investigating several topics connected with stellar evolution ; for example the age or distance can be more accurately determined than for field stars .
However , one important parameter , the metallicity , is only known for a marginal percentage of open clusters .

Aims : We aim at a consistent set of parameters for the open clusters investigated in our photometric \Delta a survey of chemically peculiar stars .
Special attention is paid to expanding our knowledge of cluster metallicities and verifying their scale .

Methods : Making use of a previously developed method based on normalised evolutionary grids and photometric data , the distance , age , reddening , and metallicity of open clusters were derived .
To transform photometric measurements into effective temperatures to use as input for our method , a set of temperature calibrations for the most commonly used colour indices and photometric systems was compiled .

Results : We analysed 58 open clusters in total .
Our derived metallicity values were in excellent agreement with about 30 spectroscopically studied targets .
The mean value of the absolute deviations was found to be 0.03 dex , with no noticeable offset or gradient .
The method was also applied using recent evolutionary models based on the currently accepted lower solar abundance value Z \sim 0.014 .
No significant differences were found compared to grids using the former adopted solar value Z = 0.02 .
Furthermore , some divergent photometric datasets were identified and discussed .

Conclusions : The method provides an accurate way of obtaining properly scaled metallicity values for open clusters .
In light of present and future homogeneous photometric sky surveys , the sample of stellar clusters can be extended to the outskirts of the Milky Way , where spectroscopic studies are almost impossible .
This will help for determining galactic metallicity gradients in more detail .