## 1 Introduction  
In current conservation practices, the use of biocides is still the most popular method in cleaning procedures for different biodeteriorated artefacts. However, the strong negative impact of these chemicals on human health, object surfaces and ecosystems are pushing researchers and conservators to find alternative solutions that are selective against biodetetrogens and at the same time environmentally friendly and safe for humans. Moreover, the choice of ecofriendly biocides is led by the EU regulation U Directive 98/8/EC, which recommends the withdrawal from the market of biocides harmful to humans and non-targetorganisms. Alternative products involve the use of natural molecules, such as, for example, plant derivates [1; 2].  
In particular the essential oils (EOs) obtained by distillation or pressing of aromatic plants are well known for their bactericidal and fungicidal properties [3]. They are mixtures of volatile compounds, insoluble in water but soluble in organic substances, characterized by low molecular weights and strong odors [4]. Their antimicrobial activity is due to their bioactive compounds such as phenols, quinines, and tannins, acting through various mechanisms, such as modification of the membrane structure or alteration of the enzymatic activity [5].  
Today EOs are widely used in the food processing, phyto-sanitary, pharmaceutical, and cosmetic sectors [6; 7; 8]. Moreover, in recent years, a large number of studies have investigated the use of EOs for the control of microbial colonization on cultural heritage surfaces [3].  
Oregano (_Origanum vulgare_) proved to be effective against fungi isolated on wood and stone artefacts [9; 10]. Clove (_Syzygium aromaticum_) and garlic (_Altium sativum_) oils proved potent antimicrobials against different fungal species including _Aspergillus niger_[11].  
Methodologies of application of EOs to the surfaces vary, and in almost all cases they imply a direct contact between oils and artefact surfaces, such as the application by brush, with packaging or padding methods or in a thickening solution (e.g., cellulose and/or sepiolite) [12].  
EOs' roles as antimicrobial agents have been tested on paper documents [13; 14; 15], historical textiles [16], wooden and stone artefacts [17; 18], and also on objects of large dimensions [19]. [PERSON] and [PERSON] [20] evaluated the effect of some EOs on fungal infestation on simulated painting models. However, despite the increasing interest, EOs have never been applied on real oil paintings. This is not surprising, as by coming into contact with pigments, EOs could act as a solvent and cause irreversible damage on painted surfaces. Citrus essential oils are in use in some \"green\" cleaning formulations and are known to have powerful solubilization abilities [21; 22]. Moreover, paintings possess a multi-material nature (sometimes with unknown composition due to the artists having prepared their own blends), and their reaction with EOs might be unpredictable.  
We hypothesize the possibility to use the volatile organic compounds (VOCs) of the essential oils for the cleaning procedure used on oil paintings, in order to avoid direct contact between the EOs and the painting surface. In the present work, the isolation and identification of the fungal and bacterial taxa from stained areas on the obverse and reverse surfaces of an oil painting on canvas were conducted, and the antimicrobial activity of oregano and cloves EOs were assessed against the isolates. Moreover, oregano EO was also tested using its volatile components only. Even if this is a preliminary Proof of Concept work, aimed to verify if indeed the VOCs of the EOs could have a significant inhibiting action on biodeteriogens of oil paintings, it can open up new ways to preserve oil paintings.