Phytate - Treatment

Birgit Reissland, Karin Scheper and Sabine Fleischer (2007)

Preparation of a rigid support

> Aim: The wet object is very susceptible to any damage caused by handling. Especially ink corroded areas are fragile. Using a rigid support prevents bending of the object and reduces the risk of crack formation or loss of fragments. The object should not have direct contact to the rigid support but instead should always lay on a polyester or polypropylene spunbond fabric like Hollytex®. The support makes it possible to remove the object from the Plexiglas when necessary.

 

> Procedure: A sheet of Hollytex® is attached to the Plexiglas with double sided self adhesive tape. The object is placed on the Hollytex

 

 

 

 

Pre-wetting with alcohol

> Aim: The absorption test is an indication how a paper will take up water. Because of the high surface tension of water, pre-wetting of ink corroded papers can be quite problematic. Ink corroded areas can be so much degraded that they do not take up water easily, they are hydrophobic. Usually, those areas are dark brown discoloured on the reverse side of the paper and are quite brittle or already have (micro) cracks. Direct adjacent paper areas are usually degraded as well, and react hydrophilic, they take up water easily. Hence, wetting an ink corroded paper with water creates stress between hydrophilic and hydrophobic areas. Crack formation along the ink lines or even further losses in ink corroded areas is the result. Therefore, an optimized pre-wetting procedure is crucial. To minimize the risk of unequal wetting, the paper is pre-wetted with an alcohol like Ethanol or Iso-propanol. These alcohols have a much lower surface tension and mix well with water. For this reason a subsequently applied aqueous solution will penetrate the paper faster and more homogeneously.

 

> Procedure: The solution (either Ethanol or Isopropanol or a mixture of the alcohol and water) is sprayed onto the object until the object is completely wetted. The object should already be placed on the Hollytex on the rigid support.

 

Treatment with water

> Aim: Ink corroded artefacts are treated with the intent to remove and/or inactivate detrimental components and discoloured degradation products. The most detrimental components are invisible but water soluble: transition metal ions like iron(II) ions or copper(I) ions and sulphuric acid. These components can be removed to a certain extent by aqueous treatments. Most effective are distilled or demineralised water. Using these water qualities bears however a risk: ink bleeding and removal of components that actually should remain in the paper like calcium carbonate (Reissland 2001). To reduce this risk it is recommended to use water that already contains one or more salts like tap water of good quality or re-calcified water (demineralised water with a small content of calcium carbonate). Addition of alcohol (e.g. ethanol) facilitates homogeneous wetting of paper and reduces the risk of bleeding of water soluble components.

> Procedure: Directly after the pre-wetting step, the objects are immersed in tap or re-calcified water. The first immersion bath should contain some ethanol. The most effective removal of soluble components is achieved when the objects are covered with water within the tray.

 

 

Left: Transfer of the pre-wetted objects into the treatment solution
Right: Tap water or re-calcified water with some ethanol are used for the first immersion

 

Soluble and discoloured components dissolve into the surrounding treatment solution until an equilibrium is reached. When the water is saturated and can not take up more dissolved components it is time to change the treatment solution. Depending on the amount of water and soluble components, this is reached after 5-10 minutes. Some objects can not be fully immersed because they are too fragile or contain potentially soluble media. In those cases, an experienced paper conservator will choose an appropriate application method like float washing or spray treatment on a suction table.

 

 

 

Left: Transfer of the pre-wetted objects into the treatment solution
Right: Tap water or re-calcified water with some ethanol are used for the first immersion

After 5–10 minutes the objects are transferred into the next tray that contains fresh tap or re-calcified water. If necessary, this solution also can contain some ethanol. The water should be continuously exchanged until all (visible) products are removed.

 

 

 

Left: Transfer of the objects to the next treatment solution
Right: Immersed objects are surrounded by water and have no contact to the Hollytex® support

This can be done either by a continuous water flow or by transfer of the objects into trays with fresh water. The procedure can take 30 minutes or longer. Determination of the effective removal of soluble components is possible by measuring conductivity of the solution. Most workshops do not have the necessary equipment and therefore must rely on visual impression and personal experience. The washing treatment requires time. If it is done not properly, the next treatment steps are less effective.

 

 

 

Left and right: Continuous exchange of the treatment solution

Treatment with calcium phytate solution

> Aim: Even if theoretically all iron(II) ions are removed by a thorough treatment with water, the paper still contains free iron(III) ions that are not water soluble and need to be inactivated. That is the reason why a calcium phytate treatment is carried out. A calcium-phytate complex can exchange calcium ions for iron(II) and iron(III) ions and form iron-phytate complexes. As long as iron ions are part of the iron phytate complex they can not catalyse oxidation anymore (Neevel 1999). Iron phytate has a white colour. Also, calcium phytate can exchange calcium for copper ions and form copper phytate. Such complexes however do not inactivate the copper ions. Copper phytates are water soluble and can be removed by subsequent aqueous treatment.

 

> Procedure: If all (visible) components were removed by washing in water, the objects are transferred into the next treatment solution: calcium phytate. First, the pH of the solution should be determined – pH values of 5,2 - 5,8 are recommended. The solution might contain some white precipitation of calcium phytate that is inactive and does not react.

 

 

 

Left: pH determination
Right: White calcium phytate precipitates within the solution

 

The objects are transferred on the rigid support into the calcium phytate solution. They should be surrounded by the treatment solution. During the immersion treatment, calcium phytate exchanges calcium ions for free iron(II) and iron(III) ions and forms iron-phytate complexes. The iron-gall ink remains intact.

 

 

 

Left: Objects are transferred into the calcium phytate solution
Right: Objects are surrounded by the treatment solution

 

The duration of a calcium phytate treatment differs for each object. To check whether the treatment was sufficient, an iron(II) test can be carried out. The first check should be done after 10 minutes. For this test the rigid support is lifted until the object is above the solution. A dry piece of iron(II) indicator paper is brought into contact with an ink line. The dry paper will suck up some solution. For correct interpretation, the test strip is put on a white filter-paper background. A magenta colour indicates that iron(II) ions are still present and the treatment must be continued. The treatment should be finished when the iron test is negative.

 

 

 

 

 

Left: The object is lifted above the treatment solution, dry indicator paper is applied
Right: The indicator papers are compared on a white filter paper

 

> Take care: Sometimes the iron(II) test remains to be positive even after a long immersion time in a calcium phytate solution. Reason can be that too much objects have been treated and that the treatment solution is “used up”. In this case treatment could be continued in a fresh solution. Otherwise some objects just contain too much free iron(II) ions. After 30 minutes a calcium phytate treatment should be finished, even if some iron ions are left. The quantity of still present iron ions might actually be quite small, since the iron(II) test is so sensitive that a light magenta colour already indicates 1ppm of iron(II) ions.
In order to check if iron(III) ions are present, the test can be modified. Present iron(III) ions need to be reduced to iron(II) ions on the indicator paper. Normally, ascorbic acid is used for this. The modification of the test using ascorbic acid should not be carried out for ca-phytate treatments, since the low pH of the ascorbic acid destroys iron phytate complexes, causing a misleading positive result. In order to avoid biased test results application of a neutral reducing agent like sodium dithionite is recommended.

 

Treatment with water

> Aim: After the calcium phytate treatment, iron phytate and calcium phytate are present within the object. If those compounds remain there, they form white crystals during drying. To prevent such crystal formation, these components can be removed during a subsequent aqueous treatment. If calcium phytate should remain in the paper as “oxidative reserve”, this treatment step should be left out.

 

> Procedure: After the calcium phytate treatment, the object should be rinsed for some minutes in tap water or re-calcified water.

 

 

 

Left: Objects are transferred into the water
Right: Objects are surrounded by the treatment solution

 

Deacidification with calcium bicarbonate

> Aim: After treatment with several aqueous solutions, most of the free acid is already dissolved and removed. In order to prevent acid catalysed hydrolysis in the future, remaining acid should be neutralized and an alkaline reserve left in the paper. Calcium carbonate is recommended since pH values reached during and after treatment are in a safe range and do not exceed pH 8.5. Higher pH values are of risk to the inks and should be avoided. Therefore, using magnesium bicarbonate is not recommended.

 

> Procedure: For deacidification, the object should be immersed for 20-30 minutes in a saturated calcium bicarbonate solution.

 

 

 

Left: Calcium bicarbonate solution is used directly from the fridge
Right: After a while, the objects are transferred into the calcium bicarbonate solution

 

> Take care: When the calcium bicarbonate is self-made with mineral water, air bubbles tend to be formed when a paper is put into the solution. The air bubbles are underneath the paper and create tension and inhomogeneous treatment. The amount of carbonic acid in the mineral water differs per producer. Water from “Bar Le Duc” contains considerably more carbonic acid than water from “Spa” and forms more air bubbles. Only mineral water free of iron- or copper ions should be used.

 

 

 

Left and right: Air bubbles can be formed underneath the object

 

Pre-drying

> Aim: After a thorough calcium phytate / calcium bicarbonate treatment, the object should be pre-dried. This pre-drying step is necessary to achieve an effective surface sizing.

 

> Procedure: The objects are taken out of the calcium bicarbonate solution. The Hollytex® support is de-attached from the Plexiglas by taking off the double sided tapes. The objects are covered with another sheet of Hollytex® and pre-dried between natural felts under some weight. If a suction table is present in the lab, this pre-drying step can also be carried out on the suction table and directly continued with the surface sizing. Best results are achieved, if the object is still damp, not dry.

 

 

 

Left: The objects are taken out of the calcium bicarbonate solution
Right: The Hollytex® is detached from the Plexiglas

 

 

 

Left: The objects are covered with another sheet of Hollyex® 
Right: Slow and homogenous pre-drying is achieved between Hollytex® and natural felts

 

Surface sizing

> Aim: As a rule of thumb, historical papers with a suitable surface size today are in good condition while ink corroded papers usually are badly sized. The applied glue obviously plays a protecting role and forms an intermediate film between the paper and the ink. During the various aqueous treatments, the water-soluble glue of historically papers is presumably (partly) removed. Application of a new surface size offers several advantages: a protecting film is added between the atmosphere and the surface of ink and paper and the paper gains mechanical strength and flexibility. Moreover, certain gelatines are capable to enclose iron ions under certain conditions.

 

> Procedure: Before sizing it must be decided, on which side of the object the paper repairs are to be applied. The damp object should be taken out of the drying sandwich and put on a Melinex film or a Hollytex® support. The side where no repairs are to be made should be sized first - either by spraying or by applying the size with a soft brush. A second sheet of Melinex / Hollytex® is put on the object. The object is turned, the upper protection is removed and it is sized from the side where the repairs will be done.

Mending

> Aim: Cracks and little losses in the paper are fragile and bear the risk of further decay. Mending will support these areas and prevent further losses. The proposed method is fast and has one major advantage: areas that are already very fragile are mended in one step together with the re-sizing procedure. Since no other adhesive needs to be applied locally, local stresses in endangered areas are minimized.

 

> Procedure: The just sized and still wet object is put on a light table with the side face up where the repairs will be done. Already prepared strips of Japanese paper are applied on cracks and losses. The Japanese paper is dry and sticks immediately to the wet surface. If necessary local areas can be re-wetted with gelatine to guarantee optimal attachment.

 

Drying

> Aim: The objects should dry as homogeneously as possible. Local tensions should be avoided.

Procedure: The mended objects are put between dry and clean Hollytex® sheets and dried between natural felts under pressure