||Research and treatment (2006)
creator(s) S.M.A.K., Ghent
contributor(s) ICN, The Netherlands
1. ELEMENTS OF THE AEROMODELLER
1.1 The balloon
Materials and construction
The PVC balloon has an elongated, symmetrical form. The fuselage, an elongated oval chamber, 28 meters long and with a diameter of six meters, is composed of some thirty bands of 0.5 mm thick polyvinyl chloride foil that are adhered to one another. The seams are reinforced and the entire assembly is hung up with 52 brackets and nylon ropes. Descending from the middle of the bottom of the fuselage is the plastic piping that leads to the engine in the cabin.
The plasticized polyvinyl chloride (PVC) used by Panamarenko to create the Aeromodeller has been one of the most commonly used plastics materials since the 1950s. PVC is a chlorinated hydrocarbon polymer which is polymerised from vinyl chloride via a free radical induced addition reaction.
To increase the workability, flexibility and elongation of the material, PVC film is commonly plasticized with di-(2-ethylhexyl)-phthalate (DEHP) in ranges varying from 17-30% by weight.
The degradation of materials used for the balloon, such as PVC and synthetic adhesives, is caused by light, oxygen, moisture, mechanical stress, high temperatures and contact with aggressive agents. The degradation of PVC is characterized by discolouration of the polymer from white to yellow, red, brown and eventually black. The degradation leads to changes in initial physical properties and also loss of plasticizer, which takes place linearly with time.
Several PVC repair patches had already been attached in the middle and bottom of the balloon, and also where the air tube is connected. By comparison with the ends of the balloon, these middle and lower sections of the PVC film were more degraded, having turned a characteristic translucent yellow colour. Temperature, light and mechanical stress had clearly had a greater effect on these sections of the fuselage.
The balloon had always been folded during storage and transportation. A pattern of brown lines along these folds was also present. This was due to the greater degradation of the PVC along the folds than elsewhere. A layer of superficial dust was clearly visible on the inside and outside of the PVC surface. This dust layer had been caused by the environmental circumstances during exhibition and had also been blown in by the engine inflating the balloon.
1.2 The ventilator fan for inflating the balloon
The ventilator fan used to inflate the balloon between 1971 and 2002 is a VOG type 4VBC 714, 230V mono 2.9 AMP, 0.37 kW, 50 Hz, speed 1410 RPM. It is made of metal and is painted grey.
During the exhibition in Brussels (Sept 2005 - Jan 2006) the balloon was inflated by a new ventilator. This same ventilator was also used for the air bows during the restoration process [HADEK, AOM0150 (EU), 220 – 240V, 1.1 kW, 1.5 HP, speed 2800 RPM, product A0004 GB0]. The new ventilator is controlled by a frequency regulator, which governs the speed of the air. This ventilator is in compliance with the security norm and will be a good solution for inflating the balloon in the future, as well.
1.3 The gondola
Materials and construction
The gondola was designed with all the facilities needed for a comfortable journey. The inhabitable inner space of the cabin has a surface area of six by three meters and it is propelled by four servo engines with propellers, by means of which the structure can be turned in all directions. On top of the gondola a wooden framework is attached, onto which the engines and gasoline tanks are fastened. The elongated balloon is bound by ropes to the wooden framework and the cabin.
Panamarenko experimented with a variety of materials for building the cabin, including reeds, bamboo, rushes, cane, palm leaves. The cabin has to be strong because it also serves as landing gear. It also needs to be flexible and not heavy. Because it is not possible to weave bamboo, Panamarenko opted for cane. There are 250 different types of cane. Panamarenko used the stem of a crawling cane with an external layer (bark) that is hard and smooth. Specialised basket weavers from Bornhem did the weaving. In collaboration with Panamarenko, they produced the different panels and attached them to one another. After experimenting with white, black, blue, red and silver coloured paint, the artist chose the silver.
The gondola is made up of five sections. Each section is composed of intertwined cane panels fixed with metal plates. The gondola rests on a wooden frame with wheels on the bottom so it can be moved. The cabin is built around an internal metal structure composed of six supporting elements. Four single elements are positioned on the sides near the four corners of the gondola, and two double elements are positioned on the sides in the middle. The balloon has 52 suspension points. Nylon ropes are attached to these points in order to connect the PVC balloon with the gondola. The gondola has the following dimensions: 2.029 m high x 6.272 m wide x 3.280 m deep.
Even the structure with the motors was made by the artist: seven layers of plywood adhered to one another with epoxy resin adhesiven a fan-shaped form were fashioned into the right shape.
There are a variety of different reasons for the balloon’s degradation. The cabin was damaged during the test flight by the artist, but the repeated installations, de-installations and storage have also compromised the strength and durability of the cane. The edges of the panels were damaged by the fixing system composed of metal plates, and the free edges were broken during previous installations. Some attachment sites for the metal plates were also broken.
Some aluminium plates are present on elements 3, 4 and 5 to reinforce the structure. The surfaces of these elements were dusty and worn by environmental circumstances. There are a number of different yellow spots visible on the inside of section no. 3. These were perhaps due to a loss of fuel and a “temporary mending” is visible on the outside of the section. Certain patches of “gold aureole” are visible inside element no. 4. These stains, which are mainly present on the floor of the gondola, are due to spilled oil. Element 1 is also worn because of the action of the support structure. Different old retouches and various gaps in the woven cane panels are present on all the sections (outside and inside). Some parts of the cane panels are broken and therefore no longer solid.
1.4 The support structure for propellers and engines
The support structure for the engines is composed of two parts: a silver painted wooden frame and a metal structure. The metal structure is fixed to the wooden frame with screws. The wood used for the frame is fir. The metal structure is composed of aluminium, steel and PVC tubes. The tubes are painted silver. Wires and electrical devices are placed on this structure.
The metal structure is oxidised and dustySome cracks, scratches, dents and oil stains are present on the metal. There are also some old repairs on the structure, whichhas been repaired with polyester. On the wooden frame there are some splinters, scratches and areas where the paint has come off.
1.5 The engines with the propellers
The two engines are made of aluminium, steel and some PVC tubes painted silver. Each engine has two propellers. The propellers are made of wood. The engines and the propellers are dusty. The metal is oxidised and there are some scratches, dents and oil stains on it. There are little spots of paint on the wood.
1.6 The jerrycans
Four jerrycans are placed on a metal support structure. This structure is tied to the wooden frame above the gondola with nylon ropes. The jerrycans are made of metal (steel) and are painted green. The metal is slightly oxidised. There are some red spots (oil stains) and scratches on the surface of the jerrycans.
1.7 Heat and fire protection clothing
The gondola is equipped with two sets of heat and fire protection clothing made of asbestos. Each set is composed of an upper part (hood) to cover the head and another part to protect the body. On the upper part there is a plastic shield to protect the eyes. The hands and the feet are also protected by the textile. The protective clothing is dusty, dirty and worn. The metal fasteners and zippers for putting on the clothing are oxidised, and there are some scratches on the plastic shield.
1.8 White nylon ropes
The ropes for tying the balloon to the ceiling and to the gondola are made of threaded nylon. During the exhibition in Brussels (Sept. 2005 - Jan. 2006) 43 ropes were used: 30 to tie the balloon to the gondola and 13 to tie the balloon to the ceiling. The ropes are in good condition. Some of them are the original ropes from the 1970s, which have yellowed in the course of the years.
2. SCIENTIFIC RESEARCH
2.1 Research on the balloon
For the scientific analytical research component of this conservation project, a cooperative agreement was set up with the Netherlands Institute for Cultural Heritage (ICN) in late 2003. Around 50 samples from different discoloured adhesives and various patches and PVC films from the balloon were taken and firstly visually examined with a microscope (magnification 40 X). Research into the composition of the materials was performed using Fourier transform infrared (FTIR) spectroscopy, thermal hydrolysis and methylation pyrolysis gas chromatography-mass spectrometry (THM-Py-GCMS).
For quantifying the amount of plasticizer in the PVC films, weight loss was measured using an electronic analytical balance. To establish the influence of the various detergents and solvent gels on PVC film, PVC test pieces were submitted to Scanning Electron Microscope (SEM) analysis and photos were taken of the surface of the PVC film, before and after cleaning.
TYPE OF ANALYSIS:
Infrared spectra were performed using a Perkin Elmer Spectrum 1000 FTIR spectrometer combined with a Golden Gate, Single Reflection Diamond ATR unit, with a sample size of 0.6 mm2. Spectra were recorded from 4000 – 600 cm-1. The infrared spectra of the samples were compared with the spectra of reference materials.
2. TMH-Py-GCMS (Thermal Hydrolysis and Methylation Pyrolysis Gas Chromatography-Mass Spectrometry)
The pyrolyser used was a Curie-Point Pyrolyser from Horizon Instruments. The pyrolysis temperature was 625ºC (Dekker 1995). To increase the pyrolysis yield and to enhance chromatographic separation, post-pyrolysis thermal hydrolysis and methylation with tetramethyl ammonium hydroxide (TMAH) was used. Owing to the TMAH, the polar components of rubber adhesives are methylated. The GC-MS used was a Thermo Finnigan GC8000 top-Voyager combination. The separation was performed on a ZB5 (Zebron) column with a length of 15 m, internal diameter of 0.25 mm and film thickness of 0.25 µm. The temperature program used was 40ºC (1 min) – 20ºC/min - 310°C (2 min). Mass spectral data were collected with a mass range of 40 – 480 amu and with a scan rate of 0.5 seconds. The results of the analysis of the unknown samples were compared with the analysis of the reference adhesives.
The analyses were performed in a JSM5910LV SEM (Scanning Electron Microscope, JEOL) operating at 15kV, with a low vacuum secondary electron detector (LVSE) to examine the surface morphology of selected test pieces. The pressure in the specimen chamber was 40 Pa. Samples (3 x 3mm) were adhered to aluminium stubs and examined at magnifications of 85 to 1000 X.
Peel strength test
For the adhesion of seams and large PVC insertions, four rubber based adhesives (Bostik® 1220, Bostik® 1475, Teroson® PVC and Terokal®) were selected and submitted to a peel strength test in accordance with ASTM standard D 903. The four adhesives were applied to 200 x 25 x 0.28 mm PVC test strips using an adhesive comb that produced a thin, even layer of adhesive, and then they were adhered to a glass plate. A good adhesion layer contains no bubbles and enough adhesive to acquire optimum peel strength. Before the adhesive was applied to the test strips, the PVC strips were cleaned to remove fatty substances and superficial plasticizer and then sanded with no. 100 sandpaper. Drying times of 5 and10 minutes were applied in order to let the solvent evaporate according to the application instructions for the chosen contact adhesives. The test strips were pressed onto the glass plate with a rubber roller and peeled back at an approximately 180º angle. Different weights, in ascending order, were connected to the PVC strips until failure occurred.
Peel strength test of solvent based rubber adhesives:
5 min. drying 10 min. drying
Cleaning + sanding Cleaning + sanding
Teroson© PVC 4.4 kg
half and half 4.4 kg
all adhesive on PVC
Terokal© 4.4 kg
80% adhesive on PVC 6.6 kg
Bostik© 1220 3.3 kg
all adhesive on PVC 2.2 kg
all adhesive on PVC
Bostik©1475 2.2 kg
all adhesive on PVC 1.1 kg
all adhesive on PVC
Resistance to deformation, creep test
3M® transparent Vinyl Tape 471 was used for the repair of small holes and tears. The compatibility of this tape with the PVC film was established using the creep test in accordance with ASTM D 3930 test 9, though slightly modified. Four test pieces were cut in a special shape and different weights were attached to the bottom side. The test pieces were kept at 23°C and 50% RH during the measurements. The width of the sample was measured on the middle line, the distance between the two marks was measured over time on the inside of the line mark, and the dimension changes of the tape and PVC were compared. The PVC test pieces were 0.28mm thick, and the tape test pieces were 0.13 mm thick.
Ageing due to heat and to natural and artificial light
The performance of the 3M® tape was submitted to a 70ºC heat ageing test for a period of one month in a Vötsch Vc 0200 climate chamber with 80-35% RH changing relative humidity at 3 hr intervals. Test strips with the four rubber based adhesives were submitted to light ageing in a Xeno tester with an Alpha High Energy (Atlas) filtered xenon arc lamp for up to 336 hours. Test strips, partly covered with black paper to facilitate comparison, were also submitted to daylight (on the north) in the laboratory for one month.
2.2 Results and discussion for the balloon
Results of FTIR and THM-Py-GCMS analysis of the adhesive samples from the patches of former restorations in various periods showed that in spite of the eight different discoloured adhesives observed, only three types (PVC adhesive, PUR/acryl and rubber adhesive) were used.
Adhesives, condition of adhesives and condition of PVC underneath the adhesives:
||Area on balloon
||Condition of PVC film underneath adhesive
||Observed condition of the adhesive
|Dark brown / dark red
||Bad, very stiff, breakable when folded
||Stiff and breakable
||Adhesion very poor. Lumps of adhesive on PVC film
||Acrylonitril / butadiene
rubber / polyisoprene
|Good, still flexible
||Adhesion on PVC still very good
It was noted that the PVC adhesive caused the main damage to the balloon, which is not surprising since PVC adhesives contain dissolved PVC and thus also PVC solvents, and it is these solvents that attack the original PVC film. Rubber based adhesives also contain solvents, but these are contact adhesives, which means that the solvents need to be evaporated before the PVC films are pressed together. The aged PUR/acryl adhesives were still white and opaque but their adhering strength was very poor and in some cases even zero. The original rubber adhesive is still in good condition, although slightly yellowed, and its adhesion on the PVC film is more than sufficient.
In all samples, no serious damage of the surface (SEM photos) was observed.
Adhesive and tape testing
The four adhesives tested showed good peel strength. For the Bostik adhesives, a drying time of 5 minutes gives the best result, whereas for Terokal®, the resin-containing adhesive, a drying time of 10 minutes gives better results.
Bostik® 1220 and Bostik® 1475 have nearly the same peel strength but the ease of application and the formation of less bubbles during evaporation of the solvents makes Bostik® 1220 more useful for the application of repairing loose seams.
The creep test showed that PVC film and 3M® transparent Vinyl Tape 471 are compatible.
3M® transparent Vinyl Tape 471, which contains a styrene butadiene rubber adhesive, does not yellow at all upon ageing, while all four rubber based adhesives did. Teroson® PVC and Terokal® discoloured more than the Bostik adhesives, and therefore were not suitable.
2.3 Research and results for the gondola
The analyses by the ICN revealed that the paint on the gondola is an alkyd resin (GC-MS by H. Van Keulen) with aluminium particles mixed into it (X-ray.diffraction by P. Hallebeek). The infrared spectrum (FTIR by T. van Oosten) indicates the presence of shellac and of a waxy coating coming from the cane.
3. CONSERVATION TREATMENT
3.1 SUPERFICIAL CLEANING OF THE BALLOON
The treatment started with the complete cleaning of the interior and exterior surfaces of the balloon in January 2004. Weakened seams and old repairs were readhered after surface cleaning. For the removal of superficial dirt as well as some synthetic adhesive layers, many different cleaning methods were tested. The observations and conclusions of the tests demonstrated sufficient cleaning results with the detergent Varsapon, though the best results were achieved with a 5% solution of Dehypon® LS 45 in demineralised water. Dehypon® LS 45 is a low foaming non-ionic surfactant with good moisturizing characteristics. It is used in conservation as a surfactant and moisturiser for hydrophobic surfaces such as glass and plastics, and it can be used as an alternative for the surfactant Synperonic N®. A second cleaning action with demineralised water and cotton swabs removed the residue of the surfactant.
— 100% demineralised water Moderate
— 2% Varsapon in dem. water Good; dirt can be removed completely
— 2 g Dehypon LS 45 in 99 g gedem. Water Moderate
— 5 g Dehypon LS 45 in 99 g gedem. Water Good, dirt can be removed completely
PRODUCT DATA FOR DEYPHON LS 45:
Chemical description: fatty alcohol, ethoxylated and propoxylated
Appearance: yellowish, clear to slightly cloudy liquid, specific odour
pH (1%): 6.0 – 7.5
density (g/cm, 70°C): 0.927 – 0.931
flash point: >100°C
solubility (20°C): partially miscible
turbidity temperature (°C): 20 – 22
water content (%): < 0.5
active substance (%): 99.5 – 100
hydroxyl value (mgKOH/g): 87 - 97
Dehypon can be stored below 40°C for at least 2 years. Dehypon is a low foaming nonionic surfactant with sufficient stability in alkaline media (carbonates, silicates, phosphates) and acidic media (phosphoric acid, citric acid). The technical properties of Dehypon LS 45 are not affected by water hardness ions.
3.2. Removal of the adhesives
The cleaning proposals for removing the adhesives were all based on the chemical characteristics of the adhesives identified. For removing white coloured polyurethane/acryl adhesive, 100% shellsol A100 was used. To observe the behaviour of the plastic during cleaning, additional research was conducted. The cleaned PVC film showed no loss of plasticizer when analysed using the weight loss measured with an electronic analytical balance. Some of the synthetic rubber adhesives could be removed with 100% xylene.
Very hard and stiff PVC adhesives also had to be removed. Commonly used organic solvents for restoration were unable to soften or remove the polymerised adhesive remains. Because of the evaporation of most solvents, the interaction time is not sufficient to fulfil the requirements. The use of solvent gels made it possible for a less strong solvent to interact for a longer period of time without damaging the original PVC film. Richard Wolbers’ solvent gel formulas were, literally speaking, the ‘resolving’ factor (Wolbers, 2000).
The solvent gels based on ether (Sellosolve, Ethanol, Carbopol 980® and Ethomeen C25®) produced the best results. This gel, applied with a spatula and covered with a Melinex® film, is active for a period of five hours. The adhesive parts and gel can both be removed with a brush or scalpel. After cleaning, the residue of the gel can be removed with ethanol using cotton swabs.
3.3 REPAIRING OPEN SEAMS, SMALL TEARS AND HOLES
Readhering tears and holes
For the restoration of the tears in the PVC film, tests were conducted both with adhered patches and with transparent tapes. Patches were made with thin PVC film and synthetic rubber adhesive. Small tears in the PVC film of the balloon could be restored with 3M® transparent Vinyl Tape 471. With an adhesive layer of 100 microns and a carrier layer of 130 microns, this tape is designed for sealing, patching, splicing and general purpose applications. The adhesive layer consists of a styrene butadiene rubber blend and the tape consists of a copolymer of polyvinyl chloride and ethylene vinyl acetate. The tape needs to be applied to a clean, dry and non-dusty surface. Adhesion can be improved by the application of pressure.
The original seams were readhered using synthetic rubber adhesive. During the last 30 years the original adhesive of the balloon had stayed flexible and did not become brittle, though it did yellow slightly. Panamarenko stated that he had used Bostik rubber adhesive, which is no longer commercially available (Bostik, personal communication, 2004). On the basis of the assumed characteristics of flexibility, yellowing and reversibility, a rubber adhesive was considered the best option for reattachment of the open seams. The adhesive and ageing tests demonstrated that Bostik® 1220 was the best choice and around 300 meters of loose seams were reattached.
3.4 INSERTING NEW SECTIONS OF PVC FILM
The middle part of the balloon is darker than the ends. On the ends the colour varies from translucent to yellow, including a pattern of fine brown lines. Due to the effects of temperature, light and mechanical stress, some sections of the PVC film needed to be conserved or replaced. Moreover, in some areas the film had lost all its plasticizer. The selection of the restoration PVC film was based on the characteristics of the original film. For the insertion of new sections, Claris PVC film from Alcor-Draka/ Solvay Company was used. This PVC film has a thickness of 0.4 mm and contains 30% DEHP di(2-ethylhexyl) phthalate plasticizer.
We wanted to respect the typical rib structure of the zeppelin. We worked from seam to seam, replacing highly degraded parts. The cleaned PVC was cut straight and the new parts were temporarily attached, using 3M vinyl tape. All new parts of the balloon were temporarily closed with tape. The zeppelin was inflated to evaluate its overall form. The tape was sometimes moved to improve the position of the inserted sections of PVC film. The inserted sections of PVC film were adhered with the rubber based adhesive Bostik© 1220. Some sections were also replaced from the inside.
Several options for colouring the PVC film and finding a stable colour were investigated. Inserting new sections of PVC film results in a clear visual difference between the new transparent film and the original translucent surface of the balloon. Using transparent film makes the action of restoration a visual part of the work. The artist preferred to integrate the film as much as possible into the existing work. Several options for colouring the PVC film have been investigated.
Coloured varnishes based on Paraloid B72, dispersions like Mowilith and the colourant Orasol were tested. Natural and artificial light and heat ageing tests were conducted, using the Xeno tester with an Alpha High Energy (Atlas) filtered xenon arc lamp and the Vötsch Vc 0200 climate chamber with 80-35% RH changing relative humidity at 3 hr intervals at70ºC.
Artificial light ageing test Artificial heat/ humidity ageing test
Paraloid B72 + _
Mowilith + _
Orasol colourants +/_ +
Polyurethane dispersion + _
After several colouring systems were tested, it was concluded that only Orasol gave a good result. Other systems, such as Paraloid B72 or dispersions, made the film rigid and stiff. After heat ageing, the PVC film to which the colourant Orasol had been applied was still flexible. Light ageing produced fading with some Orasol colourants, especially the light yellow coloured one.
Orasol colourants are used as printing colours, such as wood stains, and as colouring matter for epoxy and polyester resins. They are easily soluble in most common solvents. A mixture of 80% ethyl alcohol, 5% water and 15% Dowanol PM is recommended for use. The Orasol dyes are completely absorbed by the PVC film, hence the PVC film stays flexible. It was decided to prepare three different standard colours. The first and lightest colour was used for the ends of the balloon and the darkest colour was used in the middle part of the balloon. Large pieces of film were dyed with a painting roller on an extension handle.
Artificial light ageing:
1 Braun 2RL paint side, ISO6-7
2 Orange G #1 paint side, ISO6-7
3 Braun 2RL PVC side, ISO6-7
4 Braun 2RL PVC side, ISO7
5 Orange G #2 paint side, ISO6-7
6 Orange G #1 PVC side, ISO7-8
7 Gelb 2RLN paint side, ISO7
8 Gelb 4GN paint side, ISO4-5
9 Gelb 2RLN PVC side, ISO6-7
10 Gelb 2RLN PVC side, ISO6-7
11 Gelb 4GN PVC side, ISO6
12 Gelb 2GLN PVC side, ISO5
3.5 THE AIR TUBE, THE SUSPENSION POINTS AND THE BLACK LETTERS
The air hose is also made of PVC film and is attached to the balloon with a connecting piece and a long tube. It was very dirty and the connection piece was made by cutting a circle into triangles.
Originally, the air hose was positioned by the artist on one of the construction seams of the balloon. In agreement with Panamarenko, we decided to reposition the air hose, which was reconstructed and placed 30 cm from the original position.
The suspension points were seriously damaged. A support film was adhered on the backside of the suspension points. After adhering several supporting pieces of PVC film, we were able to completely close the balloon. To improve the visual aspect of the suspension points, coloured inlays were made. Different shades of coloured PVC film were made with Orasol dyes and adhered to each other with Bostik 1220 adhesive to match the discoloured degraded PVC film.
In the future, these points will no longer be used as suspension points. Their condition is too weak to carry the weight of the entire balloon. Ropes will still be attached to them, however, for the visual completion of the work.
Some text letters had detached. The original adhesive had lost its force. To reattach these black plastic films, several adhesives were tested. A tape with the same characteristics as the original was attached on a sheet of PVC film with 24 different adhesives. The effects on the PVC and the performance of the adhesives were evaluated by observing the sample under a microscope. Five adhesives gave good results. Natural and artificial light and heat ageing tests were performed on these five. Finally, a 20% solution of Paraloid B72 and ethyl alcohol (sample no. 21) was used.
Adhesives with the best result:
SAMPLE NUMBER ADHESIVE
13 20% Paraloid B72 in diacetone alcohol
14 Tape Ruban Adhesive Fabbory
17 20% Paraloid B72 in diacetone alcohol l (after evaporation of the solvent for 10 min.)
20 Adhesive spray for paper photos (Bison)
21 20% Paraloid B72 in ethanol
The gondola was cleaned with a soft brush and a vacuum cleaner. Cleaning by abrasion of the surface is better than cleaning with solvents. Mechanical cleaning is an acceptable solution for the aesthetic conservation of the gondola. The yellow stains inside the cabin were not removed. They are a kind of historical document.
The missing parts of the cane were replaced with new parts. The reintegration is important for the stability and solidity of the cabin. The missing parts were replaced with a new smaller size of cane (diameter 1.5mm). This type of cane does not have the external bark and is softer than the original cane. It is the ‘marrow’ of the cane.
The resistance of the new bamboo is inferior to that of the original. In the event of shock, it is the new cane that yields, rather than the original. The new parts and the loose splinters were adhered with an adhesive composed of Plextol 500 and 360 (w:w), for a soft adhesion. The segments are connected to each other with steel plates (total of 20 plates) locked together with old fashioned brass bolts.
For aesthetic reasons, some retouches were made on the surface to hide the damaged zones and the new inserts. Acrylic paint was used: Windsor and Newton, Finity Acrylic colour, silver, Permanence A, series 3.
The propellers and their structure were cleaned with a vacuum cleaner to remove the dust.
It would have been better to clean them, to integrate some retouches in gaps of the paint and to control the oxidation process. The wooden parts still need some treatment. It would have been good to replace some loose splinters and to retouch some gaps in the paint.