Keeping the blue: pressing larkspur, cornflower and lobelia without the fade
Blue is the colour pressing punishes most, and almost every faded sheet comes down to water left in the petal during the first two days. Here is the schedule we use to stop it.
- Collected by
- Hester Quayle
- Pressed
- Reading time
- 9 minutes
Every September someone sends us the same photograph: a sheet of larkspur that went into the press a clear violet-blue and came out the colour of weak tea. The flowers were picked at their best, laid out with care and weighted properly. What went wrong was almost always moisture, and almost always in the first forty-eight hours. Blue suffers more in the press than any other colour, but it also improves more than any other when you are disciplined about water.
The blues of larkspur (Consolida ajacis), cornflower (Centaurea cyanus) and trailing lobelia come from anthocyanins. Their colour depends on the acidity of the cell sap and on the pigment staying bound to metal ions and co-pigments inside the cell. When a petal dries slowly, the cell walls break down before the water has gone, the sap pools, and the pigment drifts towards mauve and then brown. When the water leaves quickly, the colour is fixed before it can drift. Every step below exists for speed.
Cut after the dew has burned off, around eleven in the morning on a dry day, and never within a day of rain. Choose florets that opened in the last day or two. On a larkspur spike, the lowest florets are usually already past it, even when they look fine. Strip the florets from the spike rather than pressing it whole: single florets dry in roughly a third of the time. With cornflowers, split each head in half with a scalpel straight down through the receptacle, so the thick base can’t hold water against the petals.
Build the stack from the bottom up: board, corrugated card with the flutes all running the same way so air can move through them, blotter, one sheet of 30 gsm acid-free tissue, the flowers, tissue, blotter, corrugated card, and repeat. Lay only one layer of flowers per blotter, with no florets touching. Apply about 15 kg of weight across an A4 area, or strap the press as tight as you can turn the bolts. Then put it somewhere warm with moving air: an airing cupboard at 28–30°C, or a shelf a metre in front of a running dehumidifier.
Change the blotters at twelve hours, twenty-four hours and forty-eight hours. The twelve-hour change is the one most people skip, and it does the most good. By the third change the old blotters should feel barely cool against the back of your hand. Dry the damp sheets on a rack and they can be reused for years. Lobelia is usually finished in four days, larkspur florets in six, and split cornflowers in eight to ten. To test, lift a floret by one edge. If it droops at all instead of lifting flat and stiff, it goes back in.
If you need certainty and can accept some brittleness, a microwave press holds blue more reliably than anything else. We use two unglazed terracotta tiles with felt and blotter between them, run in thirty-second bursts at 50 per cent power, opening the press to let the steam out after each burst. Lobelia needed three bursts in our tests and larkspur florets four. Anything with a thick centre, such as scabious or cosmos, scorches before it dries, so keep those for the ordinary press.
Once a flower is dry, light fades blue far faster than air does. Store finished sheets in archival folders in a closed drawer with a silica sachet, and keep the relative humidity under 50 per cent. Frame behind glazing sold as filtering 99 per cent of UV. The larkspur on our studio wall, pressed in July 2023 and glazed that way, is still unmistakably blue. Its twin, framed behind ordinary float glass on the same wall, had gone grey by the following spring.