It is important to dissociate 2 processes of plant conservation : Stabilization and preservation. Stabilization takes place using living vegetals. This technique allows the plant to freeze in its state of freshness after harvest. On the other hand, vegetal preservation is done from dried plants. This process rehydrates the plant. Plant stabilization is the most reliable technique over time. It is also more expensive because it is riskier.
This is the original stabilization technique. The foot of the still fresh plant is soaked in 5 cm of stabilization solution. This solution is based on vegetable glycerine, water, food colouring and nutrients. Glycerin helps to retain water inside the plant and the food colouring gives the desired colour. Nutrients are used to nourish the plant during the stabilization process, which lasts a few days. After absorbing this substitute sap, the stabilized plant is put to dry for 24 hours. Each plant species has its own specificities: The temperature of the stabilization solution, the duration of absorption, the harvest period or the nutrients used are all factors that ensure the success of stabilization for each species. This technique, considered to be the most noble, makes it possible to obtain new colours of foliage, while preserving the natural colour of branches and stems. They are generally thicker and do not allow the dyestuffs to flow to the surface. Stabilization by capillary is also used for certain flowers such as statice, by simply stabilizing the stem, the flower being naturally dry.
This is the most common technique for flowers stabilization. Flowers must be extra fresh for a successful stabilization. Some flower varieties are ideal for this type of stabilization. This technique consists of two steps of immersion. The first bath consists of immersing the flower for 24 hours in a pure alcohol solution. The aim is to dehydrate the flower while maintaining its original shape. During this first bath, it also loses its original colour. The second bath consists of alcohol, propylene glycol, glycerin and food colouring agents. Propylene glycol and glycerin, under the catalytic effect of alcohol, are responsible for rehydrating the flower. Food dye give it the desired colour. Flower heads are stabilized without their stems because they would then take on the colour of the flower.
Contrary to stabilization techniques, preservation by immersion is carried out on dried plants. The process consists of immersing the plant in a preservative solution based on vegetal glycerine, water and food colouring to rehydrate it. This solution must first be heated to above 40°C minimum. The process then gives it new flexibility and the desired colour. Once out of the bath, these plants are cleaned and dried. The drying time can greatly vary from one specie to another, depending on the more or less spongy nature and/or porosity of the concerned plants. This technique, which is cheaper and riskier, remains less reliable over time. The conservation quality obtained by this method is not comparable with that obtained by stabilization techniques. In the case of mosses, this technique is the only reliable and valid but requires drying times that can significantly increase production costs. The lichen is immersed in a saline solution. This has the advantage of being non-flammable (unlike glycerin) and naturally treated against insects. However, it dries under 40% humidity in the air. The lichen stabilization with salt makes it the most reliable vegetal of all the preserved plants.
This technique is pretty much identical to immersion preservation. It is also used on a dry and often flat plant material. It consists of spraying a preservation solution based on vegetable glycerine, water and food colouring directly onto the plant to rehydrate it on the surface. This is particularly the case for flat and ball moss, for which this process is commonly used. The process then gives it a new flexibility on the surface and the desired colour. Once sprayed, these plants are dried only. The drying time here is much shorter than with full immersion. This technique is therefore even less expensive and risky than the previous one but has the same reliability problems over time. The conservation quality obtained by this method is not comparable with the one obtained by stabilization techniques.
Some plants can be stabilized by combining several techniques. For example, it is possible to dehydrate the plant in an alcoholic bath and rehydrate it in a hot glycerin bath without catalyst or propylene glycol. A fresh plant can also be immersed in water, considering that it will still be able to absorb glycerin by capillary in the bath. It is not uncommon to combine capillary stabilization with immersion to make the exterior colour more reliable. It is also possible to ensure the plant's resistance by stabilizing by capillary and then giving the colour by immersion. New and innovative stabilization techniques are being developed. Some, such as CO2 under pressure, offer the possibility of stabilising new species. Above all, they reduce the time needed to stabilize flowers and plants. Plant stabilization is only at its genesis. Knowledge and techniques in the field are constantly evolving.