Updated: Sep 1, 2022
One of the many glories of botanical eco printing is its element of surprise ... we use sustainable natural processes which seem to have their own mind at times, within certain general principles and parameters. Many of the surprises which greet us on opening a bundle or stack are pleasant and welcome. Others can be not-so-welcome!
Here are some general tips which will increase the chances of achieving successful, lasting, clear prints, but they are not a guarantee. Serendipity is always lurking, tantalising us.
In setting these out, I'm not intending to suggest that prints should always be clear.. you may well want to create a more painterly effect. However, the questions I get asked most often are "why are my prints such a mess/so disappointing?" [or words to that effect]. If we know which factors affect our prints, we can knowingly vary them if we wish to. I certainly play with some of these factors when printing on paper, for example, to achieve more watery, painterly effects at times.
1. Use natural fibres
Nature’s pigments don’t like to hang around with synthetic fibres… the fibre structure just isn’t right, and doesn’t normally enable the absorption and retention of natural pigments.
There are two types of natural fibres: animal [silk, wool] or plant based [cotton, linen, bamboo, viscose, paper]. They interact differently with natural dyes and pigments because their fibre composition and structure are different. Leaves from the same plant can print very differently on different natural fibres.
Preloved plant fibres in household linen and clothing can take prints particularly well, if well prepared. Go rummaging in charity, second hand or ‘op’ shops for those gems!
Remember that some man made fibres such as viscose and rayon are made of natural fibres. Paper also takes prints relatively easily, whether made from wood pulp or cotton.
2. Scour your cloth
The textile manufacturing process, particularly for many plant-based, cellulose fibres, can be heavy, leaving miniscule particles of grit and grease in the cloth.
For good clear prints, your cloth needs to be clear of all oils, grease and other manufacturing substances which can prevent the plant pigments from attaching to the fibres. This deep cleansing is known as “scouring”. There are different methods for scouring animal and cellulose fibres.
For animal fibres [silk, wool], a good wash in soap only is enough. Hand hot water is preferable, using cold water, which can save fuel, is ok. Do not use washing soda on animal fibres.
For cellulose fibres, wash in the hottest possible machine wash with neutral soap and washing soda. If you are concerned about sustainability and have access to solar power, use the hot washing machine cycle when the solar panels are generating. In any case, scouring batch at a time is the most ecofriendly way to use your machine for this. Alternatively, cover your cloth with water in a large pan with neutral soap and washing soda, bring your to the boil slowly and simmer for about an hour. You will be really astonished at how filthy the water becomes, even with fabric allegedly ‘prepared for dyeing’ [PFD]. Preloved fabric also needs to be scoured, to remove detergent deposits which could impair the natural printing process.
With paper, it’s important to be clear about any sizes or other finishing which has been applied, but no need to prepare before using.
3. Use an appropriate mordant, if needed
Most plant pigments need some help in attaching to fabric by the use of ‘mordants’, which form a bond with both the pigment and the fabric, effectively binding them together. The most commonly used mordants are water soluble metal salts: alum [which also brightens colours], iron [which ‘saddens’ pigments and/or modifies their colour] and copper, which can give a yellowish hue to pigments.
Mordants can be applied by various methods. Fibres may be soaked in the solutions of chemically derived mordant powders, and the excess moisture wrung out [see below]. Alternatively, the pot used may provide the mordant if it is made of iron or aluminium. In the case of iron, it may also be applied to the dye bath or steam by adding found pieces or rusty water to the mix.
Natural mordants include some tannins, such as from oak galls or sumac leaves, and oxalic acid from rhubarb leaves which can be toxic. They can be extracted by simmering the plant matter in a well ventilated environment .
Tannins can occur in high concentrations in some leaves, and may act as a mordant for other pigments whilst also printing strongly themselves [eg onion skins, tea leaves, blackberry foliage, eucalyptus]. However, many tannin-rich leaves are best used at least with an iron mordant to give definition to the prints, because the iron and tannin interact to form a permanent dark substance, iron [or ferrous] tannate, which makes the marks.
Soya milk can help bind leaf pigments to cellulose fibres, but is technically not a mordant. For more details, see Rebecca Desnos
By the way, vinegar is technically not a mordant.. its acidity can brighten colours and make fibres more receptive to pigments, but it does not help pigments to fix per se.
4. Know your leaves!
It’s crucial to realise that every leaf does not print, or print well. Botanical eco printing uses water soluble pigments in leaves, but not all leaf pigments are water soluble.
Most leaves have clearly different upper [sunny] and under [moon] sides, but for a few such as eucalyptus, both sides seem pretty much the same. Natural pigments and tannins are more likely to print from an obvious ‘moon’ side of a leaf, which is porous and normally has a thinner skin than the 'sunny' side. Of over 800 varieties of eucalyptus, a few will print within around 90 minutes, but many need to be soaked before simmering or steaming for several hours before releasing their tannins.
Leaf pigments vary with the season and with the environment in which they grow. Pigment colours change with the acidity and mineral content of both, the natural environment where the plant is growing, and the printing environment. Leaves from the same plant may therefore produce very different prints in May, compared with September, and in Lancashire compared with Lucerne.
There's no substitute for sampling your foliage with different mordants [and combinations of mordants] and keeping copious, detailed notes. Take note of the time of year and the location.
Some botanical eco printing Facebook sites have files with lists of leaves which are generally known to give good prints. By all means refer to theses, but always check your own foliage, and don't just sample plants and trees known to print well. You may get some lovely surprises if you venture off the standard list and experiment with other plants.
However... an important note of caution... make sure you know what you are printing with and that it is safe to work with! Remember that some plants are toxic.. Deadly Nightshade is called that for a reason. If you are unsure what a plant is, identify it before working with it. Wear gloves and be careful not too breathe in toxic fumes. There are now several smart phone plant identification apps which can help you. And you can always check the USA's Food and Drug Adminstration's Poisonous Plant Database 
5. Not too wet
Moisture is important to enable the water-soluble plant pigments to transfer to, and penetrate, the target cloth. Make sure that your fibres are thoroughly "wetted out" by soaking them. However, too much water will act as a barrier, preventing the pigments from attaching to the fibres, and as natural plant pigments are water soluble, they will waltz around in excess moisture and create fuzzy prints.
It’s a matter of judgement, learnt largely by trial and error, as to whether your target cloth or blanket is too wet. Having wetted out and mordanted your cloth [if required], wring or squeeze it out as hard as you can, without distorting it. It should just feel moist, not wet, on your skin.
6. Not too dry
If the target fibres are too dry, the plant pigments will not print and fix. They need an appropriate amount of moisture. Again, it’s trial and error and personal judgement. However, it's important that mordants and/or tannins and dyes are not applied to dry cloth.. the uptake may be patchy and uneven unless the cloth has been thoroughly wetted out and then wrung or squeezed out to be only moist.
In a hot environment, keep a close eye on your target fibres to ensure that they’re not drying out, and spray them lightly with a spray mister before placing your foliage if necessary.
7. Tight contact between fibre and foliage
Whether you are processing your bundles or stacks by submersion or steaming, tight contact is essential for clear prints so that there is nowhere for those water soluble pigments to waltz off to, once they are released from the foliage.
Saggy cloth in loosely rolled bundles will produce indistinct prints with creases and folds. Make sure that your cloth is smoothed out and tight on your bench, with no wrinkles. I often pop a large bowl or small bucket of water [or a person!] on the end, to keep the cloth tight. Roll slowly and tightly, pressing down as you roll.
Stacks of paper or cloth need to be clamped or bound tightly between tiles or blocks of wood, or pressed under heavy weights to secure the best possible contact between fibre and foliage. I like to use T-shirt yarn or elastic bandages for binding bundles or stacks, as they stretch and can create good pressure whilst also being kind to the hands.
8. Apply heat carefully and keep an eye on it!
Heat is essential to release the natural pigments from the foliage and enable them to transfer and fix to the target fibres. Heat alone will not be enough for most plants and pigments. Unless they are ‘substantive’ and very high in tannin, they will need a mordant to enable them to fix and be wash- and light-fast in the fibres.
However, too much heat .. whether too hot or hot for too long .. can affect the colour of some pigments and dyes.
Be sure that your heat is combined with moisture, otherwise your fibres may become too dry or even burn. When steaming bundles, it’s particularly important to keep an eye on them, to ensure that the steamer doesn’t run dry and result in burnt fibres. Similarly, when simmering bundles or stacks, make sure that they remain covered, to prevent uneven processing.
9. Use a resist/barrier
Many leaves and flowers, particularly with a strong iron mordant, will print through several layers of cloth or paper, depending on its thickness. This can be prevented by using a barrier or resist underneath the target cloth, or on top of the foliage [or on top of carrier blankets if they are used].
Avoid the temptation to use new plastic. It may be effective, but it’s an environmental disaster. Some argue that even using pre-used plastic [eg wrapping from goods] is environmentally damaging because tiny microplastic pieces rub off and create havoc through waste systems. There are biodegradable forms of ‘plastic’ such as corn or potato starch, but they need composting properly to decompose quickly.
A thick piece of cloth [a good use for those old polycotton sheets!], brown paper or baking parchment are effective barriers. Cloth barriers can be used time and again, washed occasionally. I tend to keep specific ones for use with specific [or no] dyes to prevent any cross contamination.
10. Steady as you go.. one step at a time!
Botanical eco printing is so engaging [some would say addictive], that it's really easy to let our enthusiasm get the better of us. I probably was [and still am, at times] the worst culprit. But remember that Rome wasn’t built in a day and botanical eco printing is a complex process, particularly when adding natural dyes into the mix.
Don't try to run before you can walk. Keep things simple at first, taking it step by step. Start with simple samples with different leaves and mordants [or no mordants at all] and build up your knowledge base systematically. That way, you're more likely to learn and understand what is going on, and to be able to reproduce prints with which you are satisfied, or even really pleased!
Keep notes [yes, of pretty much everything... leaves, location, fibres, mordants, processing methods and time].
Yes, it can be frustrating to see the most wonderful prints produced on social media by much more experienced botanical eco printers, but just as you wouldn't expect to drive a car independently after your first lesson, remember that you are on a journey through a complex set of natural process.
Steady as you go and you will learn systematically. Pace yourself to avoid disappointment and, equally crucially, wasting money on fibres, water and fuel. By all means experiment and play along the way, but don't expect to become an expert printer immediately.
Thanks for reading. I hope you have found these top tips useful and that they will minimise your disappointments. Take account of them, but above all enjoy your printing!
Please let me know if you find these tips useful, or have any comments/points to add. You can email me at firstname.lastname@example.org
By Maggie Naturally
25 August 2022