How to achieve darker blues

We often get asked: How do I achieve a darker blue in my cyanotype prints? Usually the straight forward answer is: If you want your prints to be darker you need to expose longer, but there are a lot of other factors other than the exposure time that can influence the final colour of your print.

How long to expose a cyanotype

Exposure time will have an effect on the darkness of the print, a longer exposure will produce darker blues. We always recommend doing a step test or trying some test strips before you expose your prints.

As a general rule when the uncovered areas of your print turn to a silvery greyish colour, you know that your cyanotype is exposed. This can take from a couple of minutes in the summer sun to 15-30 minutes on a cloudy day in the winter.

If you overexpose your print you will get a deeper blue but you can loose detail in your print especially with less opaque objects, flower petals or light transparencies.

Other factors that can influence the final colour

- Different papers will produce different colour tones of blue. Some papers are not compatible with the cyanotype process and the print will wash out completely or be very faint.
- If you haven’t bought the cyanotype solution from us and you are mixing your own, make sure you are using the right quantities of chemicals.
- Coating technique influences the end result, try double coating for a deeper blue. The more chemical you can put on your paper the darker the end result will be but do not allow the coating to puddle as this can cause artifacts in the final print.
- The papers have to be bone dry before exposing otherwise the chemicals will wash out or will be very faint. Unfortunately you can’t force this process either, you can’t use a hair dryer, they have to dry naturally. We always recommend drying the papers horizontally in a dark place overnight for the best result.
- If your negatives are dark enough you can exposure for a longer time and achieve darker blues.
- Some glass or perspex can block UV and result in a fainter image. If you suspect that this is the case you should do a test exposure without the glass/perspex.
- If your water is too alkali this will result in a lighter blue after washing out, you might need to adjust the PH of your water to slightly acidic with some citric acid or vinegar to achieve a deeper blue.
- Prints will darken a lot after the washing out process as they dry. They usually need at least 24 hours to turn into their final colour.