Table 1 Overview of conservation methods

Alcohol-ether-resin (AlEt)

Institution: Schweizerisches Nationalmuseum, Zürich, Switzerland

Treatment: Exchange of water with ethanol. Exchange of ethanol with diethyl ether. Soaking of wood with diethyl ether in resin-diethyl solution. Drying by evaporation of the diethyl ether in the vacuum vessel. Application of surface protection 3% Paraloid B72 solution in acetone

Impregnation solution: 70.7% diethyl ether, 16.1% dammar resin, 6.4% rosin, 3.2% dienol D102, 3.2% rhizinus oil, 0.4% PEG 400

Kauramin 800^® (K800)

Institution: Römisch-Germanisches Zentralmuseum, Mainz, Germany

Treatment: Bath impregnation at room temperature. Replacement of the solution when early polymerisation occurs. Curing of the impregnated wood in the heating cabinet at 60 °C. Afterwards slow, controlled air-drying. Dip in linseed oil varnish

Impregnation solution: 25% Kauramin 800^® solution (72 L resin + 210 L deionised water, 3.6 L urea, 7.2 L triethylene glycol)

Lactitol/trehalose (LaTr)

Institution: Brandenburgisches Landesamt für Denkmalpflege, Zossen, Germany

Treatment: Starting with 30% concentration. Increasing monthly in 10% steps up to 70%. Bath temperature 55 °C. After removal from the bath, the surfaces were dusted with crystalline lactitol monohydrate and dried in a heating oven over a period of 1 week. After drying, the surface was cleaned by dabbing with damp cloths

Impregnation solution: lactitol/trehalose solution (9:1) 30–70%. Addition of biocide if necessary (0,1% Bioban 404)

Polyethylene glycol (PEG 2000) one-step and freeze-drying (PEG1)

Institution: Nationalmuseet, Copenhagen, Denmark

Treatment: Starting with 10% PEG 2000 solution. Increasing the concentration up to 40% at room temperature. Freeze-drying in cooled chamber (approx. − 30 °C). Removal of excess PEG from the surface with a soft brush and ethanol. Subsequent surface stabilisation with 25% PEG 2000 solution in ethanol

Impregnation solution: PEG 2000, 10–40% solution with tap water

Polyethylene glycol (PEG 400 and 4000) two-step and freeze-drying (PEG2)

Institution: Brandenburgisches Landesamt für Denkmalpflege, Zossen, Germany

Treatment: Soaking in demineralised water. Starting with 5% PEG 400 solution. Raising the concentration in 5% steps. At its calculated final concentration, it was kept constant. Then the increase of PEG 4000 solution was continued in 5% steps up to its final concentration. Precooling of the wood to 5 °C then deep-freezing to − 25 to − 35 °C, freeze-drying in cooled chamber (approx. − 30 °C)

Impregnation solution: PEG-solution in demineralised water (PEG 400 and PEG 4000) was adapted according to the condition of the wood (PEGcon)

Polyethylene glycol (PEG 400, 1500 and 4000) three-step and freeze-drying (PEG3)

Institution: Archäologische Staatssammlung, Munich, Germany

Treatment: Soaking in demineralised water. Starting with 11% increasing to 15% PEG 400 solution at room temperature. 16% increasing to 20.5% PEG 1500 solution at 40 °C. 20.5% increasing to 27.5% PEG 4000 solution at 40 °C. Washing of the wood and wrapping in cellulose tissues. Intermediate storage in freezer (− 25 to − 35 °C) until freeze-drying. Subsequent freeze-drying in a cooled chamber (approx. − 30 °C). Excess of PEG was removed with a brush and ethanol

Impregnation solution: PEG-solution in demineralised water: 15% PEG 400, 6.5% PEG 1500, 7% PEG 4000

Saccharose (Sac)

Institution: Sächsische Landesamt für Archäologie, Dresden, Germany

Treatment: Concentrated the solution in 10% steps, from 10% up to 60% sugar solution at room temperature. Slow, controlled air-drying in microperforated bags. Removal of crystallised sugar residues from the surface with damp sponge

Impregnation solution: Aqueous saccharose solution 10–60%. If necessary biocide addition composed of 0.6%, sodium benzoate (E211), 0.5% Parmetol K40, 0.5% Quartasept Plus and 0.02% Tallofin OT

Silicone oil (Sil)

Institution: Texas University, Texas, USA

Treatment: Exchange of water with ethanol. Exchange of ethanol with acetone. Placing the still dripping wet acetone-impregnated samples in impregnation solution under normal atmospheric conditions. Triggering the polymerisation of the impregnation solution by gaseous catalyst: DBTDA (dibutyl diacetate)

Impregnation solution: 80% silicone oil (SFD1 (66%) + SFD5 (34%) − silanol functional polydimethylsiloxanes “PDMS”) and 20% crosslinker MTMS (methyltrimethoxysilane)