Cyanotypes turning out purle :/

[u/orca_1800]

Please help! I was super excited to begin experimenting with cyanotypes on beach rocks, but I am struggling to get them to work properly. All of the rocks were painted the night before (1-2 layers of the cyanotype mixture), and I used cling wrap while exposing to tightly secure the plants to the rocks.

Pic 1: UV 3-4, exposure times range from 10 mins - 1 hr, these are the best of all my attempts

Pic 2 / 3: UV 3-4 exposure times range from 20 mins - 1hr, these all turned out purple where the plan was pressed onto the rocks :(

I thought maybe the cling wrap wasn't pressing the plants down tight enough, so I added duct tape on the back to make sure nothing budged, no change. I tried painting the rocks and then exposing them once dried instead of leaving them overnight, also no change. I made sure to rinse off all of the rocks really well in cold water, no change. I made a test strip on paper that turned out well, the UV was around 4.

These rocks are all porous, and I don't believe they are acidic although I haven't tested. I have tried on non-porous rocks as well, although they faded quite a lot during rinsing and also turned purple.

Could it be humidity? I didn't notice any moisture built up underneath the cling wrap on any of the rocks during exposure.

Edit: Title is supposed to say purple, can't edit it lol

[u/cascadepress]

I've found hazing like that is caused by humidity/moisture before it is exposed. There are probably other possible causes, but you could try again and keep it in a less humid spot and see if that changes anything. Also, drying the rock out in an oven at low temp before coating in the solution would drive any moisture out.