The thermal -chemical- printing of the face value and other data on this labels makes delicate their manipulation and, especially, conservation in mid term basis. In special the excessive lighting exposure, the heat and humidity will also degrade the printing and adhesive.
 

Many and varied factors influence in the conservation of the ATMs of thermal type throughout the years ; The same process of manufacture and the ATM issue: The type of thermal paper used in the manufacture of the labels, the surface treatments and processing and very specially the malfunction of the thermal printer included inside the franking balance. But also the storage method and the climatic conditions. The images show the actual conditions of two labels of the same model and similar date of issue ; without a doubt the difference in the conservation can be attributed to the surface treatment of the label ( manufacture ), the thermal printer used and/or the conditions of conservation during these last years.

The quality of the thermal paper used in the manufacture of the labels is a key factor to determine his durability ; so the papers used in the first models, of much poorer quality, have taken step at the present time to the use of a paper of much better quality and than, therefore, it will allow the better conservation. Nowadays papers of thermal type exist already that allow one long conservation during many years without no special care, but its high cost seems to be that it disables, at the moment, its use in the manufacture of the labels.

The labels include surface treatments, as the processing with phosphorus for their recognition by the cancellation machines. In general, the models that have presented more problems of conservation have been those that the surface processing or the own design occupies all the surface of the label (models 2 and 3). At the present time already all the ATM designs include a white strip in the inferior zone for the printing of the face value and other data. 

The printing of the data that appear in the ATMs makes through a thermal printer lodged inside the franking balance. The paper of the label incorporates a layer thermal sensible for black images; the image appears between 70º and 80º, obtaining the maximum density to 100º. Of course the malfunction or not of the printer is equally basic to obtain a printing of the maximum quality and density.

In order to maintain the thermal ATMs in good condition during years, it's good to follow some recommendations :

• Like the stamps, it's necessary to keep the thermal ATMs in ventilated, well moved away dry places and of sources of heat and, of essential way in this case, without any contact with direct solar light. 
• The heat and the humidity dark the thermal paper and debilitate the printing. It's necessary to maintain the ATMs to an inferior temperature to 24,5 º C and humidity of 65 %.
• It's recommended specially to keep the ATMs away from contact with any kind of plastic film, because the chemical products that compose them can debilitate the printing very easily.
• Never keep two ATMs with the printed sides together, because the printing could trace one in the other.

A long term experiment is being carried out to know the behaviour of several identical labels (same model, franking balance and date of issue) stored with different procedures and materials ; after the first year there was no any visible difference among the labels and no degradation trace.
The options that include any type of treatment on the labels (chemical, in the surface, ...) have been excluded.

The used ATMs on the thermal type cannot be submerged in water to separate them of the paper and, therefore, it's necessary to keep them always adhered to the paper, preferably on a whole used cover.