GENERAL TERMS AND CONDITIONS FOR EXHIBITORS AT THE CONTEMPORARY ART EXHIBITION “SOFIA ART FAIR”
These General Terms and Conditions are established by the Sofia Breathe Foundation, with UIC 176472079, with its registered office in the city of Sofia and registered office address: village of Bistritsa, 4 Kapina Street, in connection with the annual holding of the Sofia Art Fair and apply to persons having the status of Exhibitors, within the meaning of these General Terms and Conditions. Unless otherwise agreed in an individual contract between the parties, these General Terms and Conditions shall constitute the complete and sole contract between the Sofia Breathe Foundation and each Exhibitor in connection with the Exhibition.
I. Definitions
Unless expressly provided otherwise, the terms and expressions set forth below shall have the meanings set forth respectively, within the scope of these General Terms and Conditions in their entirety:
1. “General Terms and Conditions” shall mean these General Terms and Conditions, which apply to the legal relations between the Organizer and the Exhibitors regarding registration, admission to participation, the presence of the Exhibitors at the Exhibition, and the display of their Works within the Exhibition.
2. “Organizer” shall mean the Sofia Breathes Foundation, with UIC 176472079, with its registered office and management address in Stolichna Municipality, Bistritsa Village, 4 Kapina Street
3. “Exhibition” shall mean the entire holding of a cultural mass event – Contemporary Art Exhibition “Sofia Art Fair,” organized by the Organizer, on all days of preparation (29.09.; 30.09.; 01.10.; 06.10.; 07.10) and throughout its holding – from 02.10.2025 to 05.10.2025 inclusive, from 11:00 a.m. to 8:00 p.m., at Sofia Tech Park, Sofia, Tsarigradsko Shosse Blvd—no—111 G, “Innovation Forum John Atanasov” building.
4. “Exhibitor” shall mean the persons who have submitted a registration form according to the template and who have been admitted to the Exhibition by the Organizer to provide one or more of their own or other authors’ Works, as specified in their application, as well as the Organizer’s requirements;
5. “Candidate” shall mean the persons meeting the requirements outlined in the General Terms and Conditions, who are interested and willing to be Exhibitors but have not yet submitted a registration form by the template or have submitted one but have not undergone consideration of their candidacy before a jury of the Exhibition Organizer.
6. “Work(s)” – shall refer to any work of visual art whose author is an Exhibitor and/or another person who has duly authorized the respective Exhibitor.
7. “Exhibition Territory” shall mean the “John Atanasov” Innovation Forum building, located at Sofia Tech Park, Sofia, 111G Tsarigradsko Shosse Blvd., with the respective adjacent and common areas, as well as the site infrastructure in front of the “John Atanasov” Innovation Forum building.
8. “Exhibition Space” shall mean a designated area of the Exhibition Territory in which Exhibitors will be able to display a corresponding number of Works by specific authors in pavilions designated for the purpose;
9. “Sofia Tech Park” shall mean “Sofia Tech Park” AD, with UIC 202099976, with registered office in the city of Sofia and management address, Mladost district, Tsarigradsko shose, 111 G, floor 2
10. “Internal Rules” shall mean the General Rules and Conditions for the use of the event halls in the “John Atanasov” Innovation Forum building and the “Laboratories” building, located in the Science and Technology Park complex in Sofia, adopted by Sofia Tech Park, with which the Organizer will familiarize the approved Exhibitors.
11. “Site(s)” shall mean the Organizer’s website: www.sofiaartfair.art.
12. “Force Majeure” shall mean any unforeseeable and/or unavoidable event which is beyond the reasonable control of the Organizer and which affects the Organizer’s ability to properly perform any of its obligations under these General Terms and Conditions. Such events include, but are not limited to, strikes, riots, acts of terrorism, fires, explosions, floods, government restrictions, lockdowns, transport bans, border closures, and other events beyond the Organizer’s control. To avoid doubt, any unilateral action by any counterparty of the Organizer, whether justified or unjustified, which prevents, frustrates, or delays the performance of any obligation of the Organizer under these General Terms and Conditions shall be deemed to be Force Majeure.
II. General provisions
1. The Organizer organizes the Exhibition with the aim of providing a platform for the performances of galleries, visual artists, creative collectives, art critics, curators, and art dealers, creating connections between collectors, museums, and a wide international audience from all over the world, and presenting to all of them the current trends in contemporary art.
2.1 These General Terms and Conditions govern the rights and obligations of the Organizer and each Applicant and Exhibitor regarding applications for participation, presence, and access to the Exhibition held and organized by the Organizer.
2.2. The Organizer undertakes to conduct the Exhibition in accordance with legal norms, the principles of good faith, and the criteria and conditions adopted in practice, consumer and/or commercial law.
2.3. The General Terms and Conditions are available to all on-site Exhibitors and third parties.
2.4. The General Terms and Conditions apply to Candidates and Exhibitors who have duly registered, as well as their employees, subcontractors, or persons who an Exhibitor otherwise engages in providing him with a service and/or other assistance in connection with the Exhibition.
3. The Organizer reserves the right to amend or supplement the General Terms and Conditions at any time. In such a case, the Organizer will make the necessary efforts to send emails with the current version of the General Terms and Conditions as soon as possible and, if possible, announce an updated version of the text of the General Terms and Conditions on the Exhibition website.
4. In case of force majeure, the organizer has the right to postpone the date of the Exhibition, shorten, extend, or cancel the venue, close it temporarily, or divide it into separate parts.
5. Each Exhibitor undertakes:
5.1. To strictly comply with these General Terms and Conditions.
5.2. To strictly comply with the Internal Rules of Sofia Tech Park, once they have been provided to him by the Organizer, as well as all legal and regulatory acts related to his activities in connection with the Exhibition.
5.3. To ensure compliance with the obligations under items II.5.1. and II.5.2 by all its representatives, employees, and/or assistants, and/or other people it has engaged to assist with the Exhibition.
5.4. If an Exhibitor fails to fulfill any of its obligations under these General Terms and Conditions, the Organizer, in addition to its other rights under these General Terms and Conditions, has the right, depending on the moment of such failure: (i) if it is before the start date of the Exhibition – to prevent the Exhibitor and/or their Works from entering the Exhibition; (ii) if it is during the Exhibition – to remove the Exhibitor and/or their Works from the Exhibition. The Organizer has the right to request assistance from the internal security of Sofia Tech Park and/or law enforcement agencies to remove the exhibitor, their works, and/or offenders from the Exhibition Territory.
III. Candidate Registration
1.1 Candidates must be legal entities or legally capable individuals, according to Bulgarian legislation, and meet one of the following conditions:
a/ be a commercial contemporary art gallery – a physical space with a central or partial focus on authors and works of contemporary art, carrying out commercial activities
b/ be a space for contemporary art – a physical space operating on a project basis with or without commercial activity, which aims to sell contemporary works within the framework of the exhibition.
c/ be a creative collective – a team of at least two visual artists and/or a curator, art historian, or art dealer
Candidates should complete a sample registration form (hereinafter called the “Application”) available on the Site.
1.2. The following data shall be provided in the Application:
a/ Exhibitor data: names, country of origin/country of registration; identification numbers, permanent address/registration address;
b/ data about the Authors (name, biography, portfolio) that the Exhibitor wishes to exhibit within the Exhibition;
c/ current contact information – address, telephone, email;
1.3.1 Submitted works specified in the Application must be originals.
1.3.2 The organizer does not allow reproductions to be among the presented works.
1.3.3. The Organizer does not require that the authors of all works submitted by an Exhibitor be alive at the date of the Application. Still, the works should qualify in the Contemporary Art category.
1.4. Exhibitors shall, at their discretion, insure the Works to be presented at the Exhibition against possible risks, including but not limited to theft, robbery, fire, flood, etc., for the period of the Exhibition. The Organizer may request proof of the insurance taken out at any time.
2. After completing the Application, it is submitted through the Site by clicking on the buttons indicated on the Site, indicating that by clicking on them, the Application is considered submitted. The Organizer will only consider Applications for which the necessary information has been sent. The organizer’s acceptance of the Application is confirmed by sending an automated message and/or e-mail to the relevant person.
3. The Organizer will send an e-mail to the respective Applicant, informing them whether it accepts, rejects, or partially accepts (for only sure Works) the Application. The Organizer sends this e-mail to the contact e-mail address specified by the Exhibitor, provided with the completed Application. In the specified e-mail, the Organizer will also inform the Exhibitor approved for participation of:
a/following stages, the conclusion of a contract, training meetings, etc.;
b/ the necessary exhibition space for displaying the approved Works;
c/ the due participation fee, determined by item IV.1. of these General Terms and Conditions.
4. By sending a completed form to the Organizer, individuals expressly agree to these General Terms and Conditions and declare that they will comply with and adhere to them.
5. The Organizer decides to admit an Exhibitor only concerning the Artists included in the submitted Application. The Organizer reserves the right, freely and at its discretion, to refuse to grant any Exhibitor access to the Exhibition and request additional information, including but not limited to the Works and their authors, to discuss changes to the list of presented works and artists. The presentation by an Exhibitor of other Artists and/or Works other than those provided with the Application and/or not selected by the Organizer is expressly prohibited.
6. After receiving confirmation under item III.3. of these General Terms and Conditions, the Exhibitor shall pay the fee under item IV.1. within the terms according to item IV.3 below. With the confirmation under item III.3. by the Organizer and the due payment of the fee under item IV.1. by the Exhibitor, a contractual relationship arises between the Organizer and the Exhibitor, with conditions, rights, and obligations of the parties thereunder, according to these General Terms and Conditions, unless the parties expressly and additionally agree otherwise in writing.
IV. Financial conditions
1. The Exhibitor whose Application for Participation is approved under these General Terms and Conditions shall pay the Organizer a participation fee, which shall be determined according to the exhibition area required for the exhibition of the approved Works. The participation fees shall be determined according to the following tariff and shall apply to the participation of Exhibitors – galleries, creative collectives
Exhibition area (sq.m.) – Participation fee (in euros)::
15 sq.m. – € 2 400
16 sq.m. – € 2 400
25 sq.m. – € 3 200
1.1. The participation fee includes the provision of Exhibition Space, the time for installing the pavilion, assembly, mounting, and placing the Works before the Exhibition, the period of holding the Exhibition, and the time after the Exhibition for removing the pavilion, disassembly, dismantling, and unhooking the Works.
– Exhibition area (H:2.65m) in dimensions specified when applying;
– lighting (50W LED, located every 1.5m);
– access to electricity;
– plate;
– window sill;
All prices are in euros, excluding VAT.
1.2. The Organizer reserves the right to unilaterally increase prices if its costs for holding and organizing the Exhibition increase, including costs to contractors, advertising, marketing, labor, taxes, fees, etc. If necessary, the Exhibitors and third parties will be notified in advance.
1.3. In the event of a subsequent need for the Organizer to provide Exhibition Space that is smaller than that paid and requested by the Exhibitor, the difference in the participation fee shall be refunded to the respective Exhibitor.
2. Information about the amount due for participation as an Exhibitor and the payment method will be provided by the Organizer to each person, together with the confirmation in response to the application for participation under Art.
3.1. The Organizer determines that 100% of the fee is due under Art. IV.1 and will be due within 14 days after receipt of the confirmation under Art. III.3 and after the conclusion of a contract between the Exhibitor and the Organizer, depending on which event occurs later.
3.3. In case of delay in payment due, the Organizer has the right to alternatively:
3.3.1. The Organizer may claim from the Exhibitor interest in the amount of the legal interest for delay, but this does not limit the Organizer from claiming damages and expenses incurred in a larger amount in connection with the delay.
3.3.2. unilaterally terminate its relations with the Exhibitor and refuse to provide him with Exhibition Space.
V. Provision of Exhibition Space
1.1 After the Exhibitor has paid the relevant participation fee, the Organizer shall provide each exhibitor with an Exhibition Space. The Exhibitors shall not have the right to choose the specific location within the Exhibition Territory and/or space where they will be located and where they will be able to present the Works, as this remains entirely at the Organizer’s discretion.
1.2. The Organizer will inform the Exhibitors in advance of the time they will have before and after the Exhibition for installing the pavilions, assembling, mounting, placing the Works, removing the pavilions, dismantling, dismantling, and removing the Works.
2. The Organizer reserves the right, at its discretion, to change the distribution of the Exhibition spaces of individual Exhibitors and the works presented by them, as well as to change the dimensions of the space provided.
3. The Organizer will expressly inform an Exhibitor who cannot be provided with Exhibition Space for reasons beyond the Organizer’s control. If the Organizer cannot provide an alternative acceptable to the Exhibitor, the Organizer shall refund the participation fee paid by the Exhibitor, and the Exhibitor may not participate in the Exhibition.
4. The Approved Exhibitors declare that they are aware that when using the Exhibition Territory, respectively, the individual Exhibition Spaces are applicable and The Internal Rules, with which the Organizer has agreed and which the approved Exhibitors undertake to comply with, insofar as they are relevant to them and/or the persons employed by them and/or otherwise engaged in cooperation with an Exhibitor.
VI. Assembling the Exhibition Space.
1.1 The Organizer and the Exhibitor will additionally agree on a convenient time at which the Exhibition Space intended for the Exhibitor will be presented and handed over to him. The Exhibition Space may be prepared by the individual Exhibitors only on the days and times specified by the Organizer, by Art. V.1.2.
1.2. The provision of the Exhibition Space by the Organizer includes:
– Exhibition panels in sizes specified when applying;
– lighting (50W LED, located every 1.5m);
– access to electricity;
– plate;
– window sill.
2.1 Any additional requirements, such as the need for further technical installations and extra space for particularly large works that Exhibitors have when displaying the Works, should be communicated and discussed with the Organizer. Individual Exhibitors will further agree with the Organizer on what additional equipment can be provided for use by the respective Exhibitor and the possibility of bringing personal equipment by the respective Exhibitor.
2.2. The organizer is not allowed to provide or approve any additional necessary technical equipment, barriers, lighting, etc.
2.3. Exhibitors monitor and guarantee that the design of the Exhibition Spaces does not violate legal provisions, these General Terms and Conditions, and/or additional instructions of the Organizer.
3. If an Exhibitor has hired a third party to assist with preparing its Exhibition Space, the Organizer must be expressly notified.
4.1. The Organizer reserves the right to inspect the Exhibition Space after it has been prepared and assembled and before the start of the Exhibition and, at its discretion, to require changes to the organization of the Exhibition Space and the Works and their removal. Any changes to the Exhibition Space must be coordinated with the Organizer.
4.2. The Organizer reserves the right to require the removal of Works that could cause a serious disturbance at the fair or endanger the safety of Exhibitors and visitors to the Exhibition through odors, noises, other emissions, or their appearance.
4.3. The Organizer may also request the removal of objects from the Exhibitors if Works are presented that were not specified in your application and/or were not admitted to the Exhibition during the subsequent inspection.
4.4. The placement and presentation of Works on flat surfaces on the floor, suspended from the ceiling, on heaters, etc., is not permitted.
5. Exhibitors may only place their advertising materials within their designated Exhibition Space. In any case, the placed advertising materials – advertising materials (business cards, brochures, catalogs of artists presenting at the Exhibition), placed in a place in the Exhibition Space, should be coordinated with the Organizer:
6. after the end of the Exhibition, the Exhibitors undertake to leave the Exhibition Territory and hand over to the Organizer the Exhibition Space in the same form and in the same manner in which it was provided to them.
7.1. The Organizer indicates, and the Exhibitor agrees that the following technical means are permitted for use in preparing the Exhibition Space:
● Chipboard screws ( No. 3 mm – 4.5 mm; min. depth in the panel – 15 mm; max . depth – 40 mm.) for attaching Works.
● Removable adhesives ( Blu Tack, etc.)
7.2. The Organizer indicates, and the Exhibitor agrees that the following technical means are permitted for use in limited quantities when preparing the Exhibition Space:
● Pencil (small markings, short lines)
● Labels – must be attached using quickly removable adhesives (above) and completely removed before dismantling the exhibition modules)
7.3. The Organizer indicates, and the Exhibitor agrees that the following technical means are not permitted for use in preparing the Exhibition Space:
● Panel pins, bolts
● Chemicals or markers of any kind
● Any gadgets not listed in 1 and 2 above.
● Any filler material to fill the gaps between the elements
● Any paint (colors) of any kind (unless confirmed or arranged with the Organizer)
VII. Media services and promotion of Exhibitors
1.1 The Organizer provides various media services to the Exhibitors for promotion, which the Exhibitors may take advantage of at their discretion, namely:
– Internet platforms with accessible photos and information about the Exhibitors;
– exhibition catalog
1.2. For this purpose, the Exhibitor shall provide the photo( s) in a suitable printed format (digital, provided via an online platform) and the texts to be printed (also digitally) on time. If this does not happen by 30.06.2025, the Organizer has the right not to include information about the Exhibitor in the Exhibition Catalog.
1.5. By sending the photos and texts, the Exhibitors guarantee that they own the necessary rights to them and provide them to the Organizer for publication in the catalog and on the Internet platform. The Exhibitors also guarantee that the photos and texts do not violate third-party rights. Suppose the Organizer incurs expenses or suffers any other damage with claims by third parties concerning the rights to these photos and texts. In that case, the Exhibitor fully compensates the Organizer for any expenses and legal fees incurred.
1.6. For inclusion in the Internet platform, Exhibitors should provide a photo of the works and texts in an appropriate digital format for display in a manner explicitly specified by the Organizer.
1.7. By sending photos and texts from the Exhibitor to the Organizer, the Exhibitor declares and guarantees that they own all necessary rights from the artist and/or photographer to allow the Organizer to reproduce, distribute, make publicly available on the Internet and publish the photos and texts through any printed or online media in art exhibition magazines, art exhibition advertisements, press releases, etc. Suppose the Organizer incurs expenses or suffers any other damage about claims by third parties concerning the rights to these photos and texts. In that case, the Exhibitor fully compensates the Organizer for any expenses and legal fees incurred.
2.1. The Organizer may provide various advertising services, including a newsletter, social networks, and participation in a podcast. If an Exhibitor wishes to take advantage of these services, he/she should explicitly declare this to the Organizer within 14 days of receiving confirmation of participation.
2.2. The fee for this additional PR package is 350 euros, payable in a manner further specified by the Organizer.
3.1. The Organizer will have the right to take photos and videos on-site to promote the Exhibition. When using the photos and videos, the Organizer declares that all personal data will be collected, processed, and stored by the provisions of the Personal Data Act, as well as the General Data Protection Regulation (Regulation (EU) 2016/679 of the European Parliament and of the Council of 27 April 2016)
3.2. By accepting the General Terms and Conditions, Exhibitors give their express consent to be photographed to create photos and videos, as well as to the use of the photos and videos taken for marketing and promoting the Exhibition,
3.3. Exhibitors undertake to obtain consent under Art. VII.3.2. also from persons employed by them and/or otherwise engaged in cooperation with an Exhibitor.
VIII. Declarations and guarantees of the Exhibitor
By confirming these General Terms and Conditions and entering into contractual relations with the Organizer in connection with the Exhibition, the Exhibitor declares and warrants that:
1. Has the proper legal capacity and capacity to enter into the contract incorporated in these General Terms and Conditions;
2. The Exhibitor owns all relevant copyright, related and other intellectual property rights, whether owned, licensed, and/or assigned, necessary to exhibit any Work admitted to the Exhibition to the public. The Organizer has the right at any time to request from the Exhibitor, and the Exhibitor undertakes to provide the Organizer with any requested evidence immediately after such request (but not later than three business days from the request), certifying that the Exhibitor fulfills the guarantee thus given.
IX. Liability. Exclusions from Liability
1.1. The Organizer is not responsible for storing or preserving the presented works, equipment, and other items owned by the individual Exhibitors.
1.2. The organizer is not responsible and has no obligation to ensure the submitted works.
1.3. The Organizer is not liable for any damages or other expenses incurred that arise or may arise for Exhibitors at the Exhibition from submitting the Application and the subsequent non-admission to participate in the Exhibition.
1.4. The Organizer is not liable for damages suffered by the Exhibitor due to Force Majeure.
2. The Organizer is not liable for any damages caused affecting the life and/or health of the Exhibitors, as well as the persons employed by them and/or otherwise engaged in cooperation with the Exhibitor unless such damages are caused by the intentional act or omission of the Organizer or by gross negligence on its part.
3. Exhibitors and persons employed by them and/or otherwise engaged in assisting an Exhibitor during the Exhibition are liable for any direct or indirect damages caused to the Organizer.
4.1. To the extent that the Organizer is liable to third parties for damages caused more than permissible and reasonable damage and has agreed to specific rules for fixing and securing exhibition equipment, in the event that a third party claims penalties or compensation against the Organizer for damages suffered, the Organizer may claim these sanctions from the Exhibitors who caused the respective damages.
4.2. According to the obligations assumed by the Organizer to third parties, the sanctions are as follows:
● Screws in the panel (per screw) – € 2
● Sticky fixing pads of any kind (foam), unless removed without damaging the panel – €5
● Self-adhesive pads of any kind (unless removed without damaging the panel) – €5
● Cut edges – €10
● Spoiled color – €15
● Stickers – €5
● Drilled hole diameter greater than 5 mm – €10
● Drilled hole through a panel with a diameter greater than 5 mm – €20
● Restore one side of the panel – €60
● Opening between panels – €10
5. The Organizer reserves the right, in the event of Force Majeure, to require the Exhibitors to bear and pay a corresponding part of the costs arising from the preparation of the Exhibition. The amount of the part of the costs to be paid by each Exhibitor is determined by the Organizer, according to the costs of preparing the Exhibition incurred up to the relevant time, which are distributed among all participants. If necessary, the Organizer will provide information on the costs incurred.
6. If the Organizer receives any material and/or non-material (including reputational damage) damages as a result of claims and/or actions by third parties and/or sanctions by administrative authorities in connection with any Work exhibited by an Exhibitor, the Exhibitor shall compensate the Organizer for all such material and non-material damages and lost profits, including any expenses related to litigation, paid administrative sanctions and the like.
X. Termination of relations with the Exhibitor
1.1. The relationship between the Exhibitors and the Organizer begins with the confirmation of the respective Exhibitor’s application and continues until the exhibitor hands over the Exhibition Space to the Organizer after the Exhibition concludes.
1.2. The Organizer reserves the right to terminate its legal relations with Exhibitors earlier in some of the following cases:
– the death of the Exhibitor or initiation of liquidation or bankruptcy proceedings against him;
– in case of delay in payment due, according to Art. IV.3.3.2.
– if the Organizer fails to obtain the necessary permits for organizing the Exhibition or the holding of the Exhibition becomes impossible, in whole or in part, for reasons beyond the Organizer’s control;
– if an Exhibitor refuses to comply with the Organizer’s explicit written or oral instructions at any time from the submission of the application for participation until the conclusion of the Exhibition;
– if an Exhibitor presents Works or authors for which he has received explicit instructions from the Organizer, he is not permitted to present.
2.1. The Organizer and the Exhibitor may terminate their relationship by mutual written consent.
2.2. The organizer reserves the right to terminate the contractual relationship if the intended or provided exhibition space can be rented by another person.
2.3. If the Exhibitor desires and requests to terminate the relationship, the Organizer reserves the right to charge the Exhibitor a penalty of 25% of the participation fee specified in item IV.1.
3. If, due to Force Majeure, an Exhibitor refuses to participate in the Exhibition, the Exhibitor may terminate the contractual relationship with the Organizer with due notice in writing sent immediately after the occurrence or knowledge of the relevant circumstance.
XI. Additional provisions
1. For issues not settled in these General Terms and Conditions related to their implementation and interpretation, the laws of the Republic of Bulgaria shall apply. All disputes arising from these General Terms and Conditions shall be resolved through friendly negotiations. If it is impossible to reach an agreement, the disputes shall be referred to the competent court in Sofia.
2. The Organizer and the Exhibitors agree that all communications between them shall be in writing, including by email.
2.1. The organizer provides the following contact details:
Region: Sofia, Municipality: Stolichna, Location: Sofia, p.k. 1000, Triaditsa district, 94 “Knyaz Boris I” Str., contact person: Suna Emel Danadzha, e-mail: office@sofiaartfair.art ;
2.2. The Exhibitor indicates, and the Organizer will accept, that the Exhibitor’s contact details are those specified in the Application under Art. III.1.1.
2.3. All communications will be deemed to have been validly sent if sent to the addresses specified above. The Organizer or the Exhibitor must notify the other party of any change in the specified addresses and/or contact persons. In the event of failure to comply with this obligation, communications will be deemed valid if sent to the correspondence addresses specified above.
3. All personal data collected both in the Application and during the Exhibition will be collected, processed, and stored by the provisions of the Personal Data Act, as well as the General Data Protection Regulation (Regulation (EU) 2016/679 of the European Parliament and of the Council of 27 April 2016)
The Executive Director of the Sofia Breathes Foundation, Suna Danadzha, has approved these general terms and conditions.