Photographed approximately 10 minutes after application of iron sulphate solution. The test samples are oak (top), pine (bottom left) and a thin piece of what I believe is cedar (bottom right). While there is strong colouration on the oak and cedar there was little reaction with pine. The photo makes it look as if the pine was bleached but that is due to the way the light is catching it - in fact there was a faint greyish-green stain effect.
On the oak the colour was a little lighter than the photo makes it appear - I would describe it as slate grey.
On the affected timbers the colour developed rapidly after application and did not deepen much, if at all, after this photo was taken. All that really happened was the samples dried out.
The solution in this test was made up with 1/2 a teaspoon of powdered iron sulphate in 10ml of water (for more details see notes with photo of powder).