European online casinos are enjoying growing popularity among Polish players, offering a wide selection of games, attractive bonuses, and modern payment methods. Foreign casinos, especially those licensed by Curaçao, Malta, and PAGCOR, offer an alternative to local platforms, providing access to thousands of titles from top software providers. Looking for the latest casinos to check out? Check out this new online casino.
This guide will provide information on the best European online casinos, bonus types, payment methods, and safe gaming practices. Remember, play responsibly – the responsibility for participating in gambling lies solely with the player.
Best Foreign Online Casinos – 2026 Ranking
Below is a list of the best European online casinos offering Polish players safe gameplay, fast payouts, and extensive bonus programs.
Detailed profiles of selected casinos
Vegazone Casino offers an impressive 260% welcome bonus up to PLN 11,500 plus 260 free spins. High rollers have a special offer of 100% up to PLN 4,300 plus 200 free spins. Additionally, players can benefit from a weekly cashback of 20% up to PLN 1,300 every Monday.
iWild Casino stands out with a 550% bonus plus 400 free spins. The platform offers a high-roller program up to USD 60,000, as well as daily 10% cashback and weekly 10% cashback, making it an ideal choice for regular players.
Lizaro Casino offers a 100% bonus up to PLN 2,250 plus free spins. The casino operates under an offshore license, likely in Curaçao, and offers a modern user interface, a good selection of slots, and a sports betting section. The minimum deposit is typically PLN 40-50, and withdrawal times are 1-3 days. Payment methods include BLIK, credit cards, e-wallets, and cryptocurrencies.
Legal Aspects of Foreign Casinos in Poland
Online gambling in Poland is regulated by the Gambling Act of 2009, amended in 2017. Legally, legal online casinos in Poland must be licensed by the Ministry of Finance. Total Casino is currently the only licensed casino in Poland offering online casino games.
Foreign casinos operate outside Polish jurisdiction and do not hold a local gambling license. Polish players can use foreign casinos, but they do so at their own risk and responsibility. Polish law does not impose penalties on individual players, but foreign operators may be subject to restrictions and bans.
European and International Licenses
The best European online casinos operate under licenses issued by renowned regulatory bodies:
- Malta Gaming Authority (MGA) – one of the most prestigious licenses in Europe, guaranteeing high standards of security and fairness.
- Curaçao eGaming – a popular offshore license held by most foreign casinos serving Polish players.
- PAGCOR (Philippines) – an Asian license held by SpiNight Casino, among others.
- Curaçao Gaming Control Board – a license held by many European platforms.
Licensed casinos are subject to regular audits and must meet specific standards regarding data security, game integrity, and player protection.
Player Responsibility
When playing at foreign casinos, remember to play responsibly. Online gambling is only permitted for adults (18+). Set time and financial limits, and do not gamble under the influence of alcohol or emotions. If you experience gambling problems, contact support organizations such as Gamblers Anonymous or the Blue Line.
The player is solely responsible for participating in gambling. Foreign operators do not guarantee the protection provided by Polish law, so always verify the license, terms and conditions, and reviews of the chosen casino.
Types of Bonuses and Promotions in European Casinos
Foreign online casinos compete for players by offering extensive bonus programs. Below are the main types of bonuses available at European online casinos for those looking for real money casinos.
Welcome Bonus
A welcome bonus is the most common form of promotion for new players. It typically includes a first deposit bonus and free spins on selected slot machines. Welcome packages can be spread over the first few deposits, offering players additional funds and chances to win.
Typical Welcome Bonus Structures:
- A single 100% bonus up to a specified amount plus free spins.
- Multi-level packages spread over the first 3-4 deposits.
- NON-STICKY bonuses that can be withdrawn without having to wager the entire amount.
- Combinations of cash bonuses with free spins on specific slots.
No-Deposit Bonus
A no-deposit bonus is an excellent option for players who want to test the casino without risking losing their own funds. This type of promotion allows you to start playing without having to deposit any of your own money.
Types of no-deposit bonuses:
- Free spins on selected slots after registration.
- A cash bonus (e.g., 20-50 PLN) to be used on various games.
- No-deposit cashback for new players.
- A bonus after account verification, no deposit required.
Cashback
Cashback is a refund of a portion of lost funds, which allows you to limit losses and extend your gaming session. This type of bonus is particularly appreciated by regular players.
Types of cashback programs:
- Weekly cashback – a refund of 3% to 20% of lost funds once a week.
- Daily cashback – smaller amounts refunded daily.
- Monthly cashback – larger amounts for VIP players.
- Live cashback – dedicated to live casino players.
Loyalty and VIP programs
Loyalty programs reward regular players with points that can be exchanged for bonuses, free spins, or prizes.
VIP program levels:
- 5-10 level systems with progressive rewards.
- 20-30 level systems for the most advanced players.
- Exclusive birthday and holiday bonuses.
- Dedicated account manager for high levels.
- Faster withdrawals and higher limits for VIP players.
Free Spins
Free spins are a popular bonus that allows you to play slots without using your own funds. They are offered as part of welcome bonuses, weekly promotions, or loyalty program rewards.
High Bonuses for High Rollers
Players who prefer higher stakes can take advantage of dedicated offers for high rollers. These programs offer significantly higher bonus limits, exclusive cashback offers, and personalized terms and conditions.
Game Types at Foreign Online Casinos
European online casinos offer a wide selection of games from top software providers. Below are the main categories of casino games available to Polish players.
Slot Machines
Slot machines constitute the largest portion of the game offerings at foreign casinos. Players have access to thousands of titles with various themes, volatility, and mechanics.
Slot Categories:
- Classic Slots – three-reel slot machines with simple rules, reminiscent of traditional fruit machines. These games are characterized by a high RTP and simplicity, attracting players who value a classic experience. Examples include Fire Joker from Play’n GO with an RTP of 96.15%, Fruit Super Nova from Playson, and Joker Stoker from BGaming.
- Video slots – modern slot machines with five or more reels, extensive bonus features, free spins, and multipliers. Gates of Olympus from Pragmatic Play utilizes the Pay Anywhere mechanic and multipliers up to x500. Sweet Bonanza, also from Pragmatic Play, offers a cascading payout system with colorful fruit and candy symbols. Book of Dead from Play’n GO is an iconic book slot with a book symbol acting as both a scatter and wild. Big Bass Bonanza from Pragmatic Play combines a fishing theme with a multiplier system and fish symbols.
- Megaways slots – slot machines with a dynamic number of symbols and paylines, offering up to 117,649 winning combinations. The Dog House Megaways by Pragmatic Play utilizes the Megaways mechanic with a Sticky Wilds feature in free spins. Bonanza Megaways by Big Time Gaming is a pioneering title in this category, revolutionizing online slots.
- Progressive jackpots – slots with a growing prize pool that can reach millions of złoty. Mega Moolah by Microgaming is the most famous progressive jackpot, having repeatedly paid out prizes exceeding €10 million. Divine Fortune by NetEnt offers three jackpot levels and a Mega Jackpot feature. Major Millions, also from Microgaming, is a classic of the genre with simple mechanics and a constantly growing jackpot.
Popular slot mechanics:
- Tumble Wins – symbols disappear after a win, and new ones fall in their place, allowing for multiple wins in a single spin. This mechanic is used in Gates of Olympus and Sweet Bonanza.
- Hold and Win – a special bonus mode in which coin symbols remain on the screen for a set number of spins. Coin Win: Hold The Spin by BGaming perfectly represents this mechanic.
- Buy Feature – the ability to buy direct entry to the bonus round for a specific bet multiplier, typically 50x-100x.
- Expanding Wilds – wild symbols that span the entire reel, increasing the chances of winning lines.
- Multiplier Wilds – wild symbols that increase the win multiplier, often combining to create larger multipliers.
TOP 5 Most Popular Slots:
- Gates of Olympus (Pragmatic Play) – Pay Anywhere mechanics, multipliers up to x500, high volatility.
- Sweet Bonanza (Pragmatic Play) – cascades, colorful graphics, multipliers.
- Book of Dead (Play’n GO) – classic book slot, RTP 96.21%, free spins with expanding symbols.
- Big Bass Bonanza (Pragmatic Play) – fishing theme, multiplier system, Fisherman feature.
- Fire Joker (Play’n GO) – classic fruit slot, RTP 96.15%, Wheel of Multipliers feature.
Table Games
Table games are casino classics, offering elements of strategy and skill.
- Roulette – available in European, American, and French versions. European roulette has a higher RTP (97.30%) thanks to its single zero, while American roulette has an additional double zero, lowering the RTP to 94.74%. French roulette features the La Partage and En Prison rules, which further enhance the player’s chances. Special variants are also available, such as Lightning Roulette by Evolution Gaming, with multipliers up to 500x.
- Online Blackjack – a card game in which the goal is to score 21 or a score closer to 21 than the dealer. Blackjack offers the lowest house edge of all gambling games, often less than 1% with optimal strategy. Available variants include European Blackjack, Atlantic City Blackjack, Vegas Strip Blackjack, Perfect Pairs Blackjack, and Blackjack Surrender.
- Baccarat – an elegant card game in which players compete for the highest hand value between the player and the banker. Baccarat is particularly popular with high rollers due to its simple rules and low house edge. Variants include Punto Banco, Baccarat Squeeze, and Speed Baccarat.
- Poker – various poker variants played against the dealer or other players. Caribbean Stud Poker offers a progressive jackpot for hitting a Royal Flush. Three-Card Poker is a fast-paced version with simpler rules. Texas Hold’em Poker allows you to play in tournaments or in a cash game against other players.
- Craps – dynamic dice games with numerous betting options, popular in American casinos.
Live Casino
Live casino combines the convenience of online gaming with the atmosphere of a real casino. Games are hosted by real dealers and broadcast live in high-quality HD or 4K.
Evolution Gaming is a leader in the live casino industry, offering a wide selection of games:
- Live Roulette – various roulette variants with professional dealers
- Live Blackjack – dozens of tables with various betting limits
- Live Baccarat – elegant tables with a squeeze option
- Crazy Time – a game show with a wheel of fortune and four bonus games
- Monopoly Live – a game based on the popular Monopoly board
- Dream Catcher – a simple wheel of fortune with multipliers
- Lightning Roulette – roulette with random multipliers up to x500
- Mega Ball – a combination of bingo and lottery with multipliers
Pragmatic Play Live offers alternative live games:
- Mega Wheel – a colorful wheel of fortune with bonuses
- Sweet Bonanza Candyland – a game show based on the popular slot machine
- Boom City – an innovative game with multipliers and explosions
The live casino is characterized by They feature professional dealers speaking different languages, a chat function with other players, and a variety of table limits, from low stakes to VIP tables.
Crash Games
Crash games are a relatively new category of dynamic games in which players bet a multiplier and must withdraw their winnings before the game randomly “crashes.”
Popular Crash Game Titles:
- Aviator – the most popular crash game, in which a plane ascends with an increasing multiplier.
- JetX – similar mechanics with a spaceship.
- Spaceman – an astronaut traveling into space with an increasing multiplier.
- Crash X – a classic version with simple graphics and fast gameplay.
Crash games are characterized by simplicity, fast pace, and the possibility of winning large multipliers in a short time.
Sports Betting
Many foreign casinos also offer a sports betting section, allowing you to bet on sporting events:
- Football – the most popular sport to bet on.
- Tennis – dynamic live betting during matches.
- Basketball – NBA and European leagues.
- Esports – CS:GO, Dota 2, League of Legends.
- Virtual Sports – 24/7 simulated events.
Top Game Providers in European Casinos
The quality of the game offerings depends largely on the software providers. The best foreign online casinos collaborate with renowned game developers.
Pragmatic Play
Pragmatic Play is one of the most popular game providers, founded in 2015 and quickly gaining a dominant position in the market. The company offers over 200 slots, live games, and table games.
Pragmatic Play’s most popular slots:
- Gates of Olympus – the flagship title with the Pay Anywhere mechanic.
- Sweet Bonanza – a colorful slot with cascades.
- Big Bass Bonanza – a series of fishing slots.
- The Dog House Megaways – a slot with the Megaways mechanic.
- Wolf Gold – a slot with a progressive jackpot.
Pragmatic Play Live offers a comprehensive live casino platform with its own game shows and blackjack and roulette tables.
Evolution Gaming
Evolution Gaming is the undisputed leader in the live casino category, founded in 2006. The company has broadcast studios in various countries and offers games in dozens of languages.
Evolution Gaming Portfolio:
- Classic live table games – roulette, blackjack, baccarat, poker.
- Game shows – Crazy Time, Monopoly Live, Dream Catcher, Deal or No Deal.
- Special variants: Lightning Roulette, Infinite Blackjack, Speed Baccarat.
- First Person – RNG versions of classic table games with 3D graphics.
Evolution Gaming also acquired NetEnt, Red Tiger Gaming, and Big Time Gaming, becoming the largest conglomerate in the iGaming industry.
Play’n GO
Play’n GO is a Swedish developer founded in 2005, known for its iconic slots and high-quality mobile games.
Popular Play’n GO titles:
- Book of Dead – the most popular book slot.
- Fire Joker – a classic fruit slot.
- Reactoonz – an innovative slot with clustered payouts.
- Moon Princess – an anime slot with three characters.
- Rich Wilde series – a series of adventure slots.
Play’n GO produces approximately 50 new games per year, maintaining a consistent release rhythm.
Payment methods at foreign casinos
Convenient payments are a key element of the online casino experience. European online casinos offer a wide range of popular payment methods tailored to Polish players.
Visa and Mastercard Payment Cards
Payment cards are the most popular deposit method in online casinos worldwide. Visa and Mastercard are accepted in virtually all foreign casinos.
| Advantages | Disadvantages |
|---|---|
| Widely available | Some banks block transactions to casinos |
| Fast deposits (instant) | Withdrawals may take 2–5 days |
| Familiar payment environment | Not all casinos accept card withdrawals |
| Transaction security | Possible currency conversion fees |
BLIK
BLIK is a revolutionary payment method in Poland, offering instant deposits without entering card details. The system works through a banking app and generates one-time six-digit codes.
BLIK advantages:
- Instant deposits without delays.
- Security – no card or account details required.
- Convenience – payments can be made directly through the banking app.
- Popular among Polish players.
E-wallets
Online wallets are fast and secure payment methods, offering instant deposits and fast withdrawals, often processed within 24 hours.
Skrill
One of the most popular e-wallets in the iGaming industry. It offers fast transactions, low fees, and the Skrill Knect loyalty program with cashback.
Neteller
An alternative to Skrill, owned by the same company, Paysafe. Similar functionalities and widespread acceptance in online casinos.
MiFinity
Growing popularity among Polish players. Offers prepaid cards and virtual cards, and the ability to hold multiple currencies simultaneously.
Jeton
A wallet specializing in casino transactions. Fast transfers, low fees, and dedicated solutions for players.
MuchBetter
A mobile wallet with a modern app. QR code payment functionality and a cashback program.
Apple Pay
Fast mobile payments for Apple device users. Highest security standards, biometric payments.
Binance Pay
A cryptocurrency wallet from the Binance exchange. Zero transaction fees, instant transfers, and support for multiple cryptocurrencies.
| Wallet | Deposit Time | Withdrawal Time | Fees |
|---|---|---|---|
| Skrill | Instant | 0–24h | Low |
| Neteller | Instant | 0–24h | Low |
| MiFinity | Instant | 0–24h | Very low |
| Jeton | Instant | 0–24h | Low |
| MuchBetter | Instant | 0–24h | Medium |
| Apple Pay | Instant | N/A | None |
| Binance Pay | Instant | Instant | None |
Paysafecard Prepaid Cards
Paysafecard is a prepaid card that allows you to deposit funds without providing personal or bank details. It’s available at kiosks, gas stations, and stores.
Advantages of Paysafecard:
- Full transaction anonymity
- Control over spending
- No bank account required
- Security – no risk of data misuse
Bank Transfers
Bank transfers are a traditional deposit method available in most foreign casinos. You can make a standard transfer to your casino account or use fast online transfers.
Advantages of Transfers:
- Security – transactions directly from your bank account
- No amount limits
- Withdrawals possible to your bank account
- No need to open additional accounts
Cryptocurrencies
Cryptocurrencies are a modern payment method offering anonymity, fast transactions, and low fees. A growing number of European online casinos accept popular cryptocurrencies.
Popular cryptocurrencies in casinos:
| Cryptocurrency | Symbol | Transaction Time | Fees |
|---|---|---|---|
| Bitcoin | BTC | 10–60 min | Medium–High |
| Ethereum | ETH | 1–5 min | Medium |
| Litecoin | LTC | 2–10 min | Very low |
| Tether | USDT | 1–10 min | Low |
| Tron | TRX | 1–3 min | Very low |
| Binance Coin | BNB | 1–3 min | Very low |
| Dogecoin | DOGE | 1–10 min | Very low |
Advantages of Cryptocurrencies:
- Instant or very fast deposits
- Fast withdrawals (often within an hour)
- High level of anonymity
- Low transaction fees (depending on the network)
- No geographic restrictions
Withdrawal speed comparison
| Payment Method | Withdrawal Time | Top Casinos |
|---|---|---|
| Cryptocurrencies | 0–1h | SpinBetter, Vavada |
| E-Wallets | 0–24h | Lemon Casino, Vulkan Spiele |
| Credit/Debit Cards | 2–5 days | Ice Casino, Verde Casino |
| Bank Transfers | 3–5 days | All casinos |
Customer Service at Foreign Casinos
Professional customer service is a key element of safe online casino gaming. The best foreign casinos offer support in Polish through various communication channels.
Communication Channels
- 24/7 Live Chat – the fastest form of contact, allowing for real-time resolution of issues. Professional casinos offer chat available 24/7.
- Email – all casinos offer email contact with a typical response time of 24-48 hours. Suitable for more complex inquiries requiring documentation.
- Telephone – some casinos offer telephone support, although this is less common in foreign casinos.
- FAQ and Help Center – extensive sections with answers to frequently asked questions about registration, bonuses, deposits, withdrawals, and account verification.
Polish Support
Polish support is a crucial element of the gaming experience for Polish players. The quality of support in Polish varies significantly between casinos.
Polish Support Levels:
- Full 24/7 support in Polish (live chat, email, FAQ).
- Partial Polish support (email only or limited live chat hours).
- Primarily in English with basic Polish support.
- No Polish support.
Security at Foreign Online Casinos
Security is the most important aspect of playing at foreign online casinos. Below are the key elements of safe European online casinos.
Gambling License
A gambling license is a fundamental criterion when choosing a casino. Safe foreign casinos are licensed by reputable regulatory bodies.
License Comparison:
| License | Prestige | Requirements | Player Protection |
|---|---|---|---|
| Malta Gaming Authority (MGA) | Very High | Very High | Maximum |
| UK Gambling Commission (UKGC) | Very High | Very High | Maximum |
| Curaçao eGaming | Medium | Medium | Basic |
| PAGCOR (Philippines) | Medium | Medium | Basic |
| Kahnawake | Low–Medium | Low–Medium | Basic |
Account Verification (KYC)
KYC (Know Your Customer) is a player identity verification process required by licensed casinos to prevent money laundering and fraud.
Required Documents:
- Proof of Identity – ID card, passport, or driver’s license
- Address Proof – utility bill, bank statement (no older than 3 months)
- Payment Method Verification – card image (middle digits and CVV hidden) or e-wallet screenshot
Verification Process:
- Verification Time: 24-72 hours (in most casinos)
- Fast Verification: Some casinos offer verification within a few hours
- Automatic Verification: Modern systems use AI for faster verification
Responsible Gaming
The best European online casinos offer comprehensive responsible gaming tools.
RG Tools:
| Tool | Description | Availability |
|---|---|---|
| Deposit Limits | Daily, weekly, monthly deposit limits | Most casinos |
| Loss Limits | Maximum loss restrictions | MGA licensed casinos |
| Bet Limits | Maximum bet per round | Selected casinos |
| Session Limits | Playtime reminders | Most casinos |
| Self-Exclusion | 1–6 months or permanent self-exclusion | All licensed casinos |
| Pause | Temporary account lock 24–30 days | Most casinos |
| Addiction Test | Self-assessment questionnaire | Casinos with good RG |
| Reality Check | Periodic notifications | MGA licensed casinos |
Advantages and Disadvantages of Foreign Online Casinos
Advantages of Foreign Casinos
A wide selection of games – the best foreign online casinos offer from 3,000 to over 11,000 games, including: Thousands of slots from dozens of providers. Extensive live casino sections.
Table games in many variations.
Crash games and other innovative categories.
Sports betting sections.
High bonuses and attractive promotions – welcome packages reaching up to PLN 11,500, VIP programs with 30 levels, weekly cashbacks up to 20%, free spins, and rewards stores.
Various payment methods – access to BLIK, Visa and Mastercard, e-wallets (Skrill, Neteller, MiFinity), cryptocurrencies, Paysafecard, and bank transfers.
Fast withdrawals – the best online casinos offer withdrawals within 0-1 hour (cryptocurrencies, e-wallets), while traditional methods take 1-5 days.
Loyalty and VIP programs – extensive reward systems for regular players, exclusive bonuses, a dedicated account manager, and faster payouts.
Mobile apps – dedicated iOS and Android apps offering full casino functionality on your phone.
Demos without registration – the ability to test games without creating an account or making deposits.
Innovative features – Buy Feature in slots, Turbo Mode, Auto Play, fast crash games.
Disadvantages of foreign casinos
Lack of a Polish Ministry of Finance license – foreign platforms lack a local license, meaning they lack the legal protection provided by Polish law.
Offshore licenses – most casinos operate under Curaçao or PAGCOR licenses, which offer less protection than the prestigious MGA or UKGC licenses.
Limited Polish language support – not all casinos offer full support in Polish, especially in live chat.
Restrictive bonus terms – high wagering requirements (often 35x-50x), time limits, exclusion of certain games, and maximum stakes when playing with a bonus.
Withdrawal Limits – Daily or monthly withdrawal limits can make it difficult to withdraw large winnings.
No Payouts on Weekends – Some casinos do not process withdrawals on Saturdays and Sundays.
Weaker Responsible Gaming Tools – Offshore casinos often offer limited Responsible Gaming Tools compared to MGA-licensed casinos.
Possible Fees – Some payment methods or casinos may charge transaction fees.
Unclear Terms and Conditions – Complex bonus and promotion terms can be difficult to understand.
Risk of Blocking – Banks may block transactions to offshore casinos.
How to Choose the Best Foreign Online Casino
Choosing the right casino is a key decision that impacts the safety and comfort of your gaming experience.
Key Selection Criteria
- Licensing and Regulation
Check whether the European casino has a valid gambling license. License information can be found in the footer of the casino website. The best options are MGA, UKGC, and Curaçao eGaming. Avoid unlicensed casinos. - Game Offer
Check whether the casino offers games from reputable providers such as Pragmatic Play, Evolution Gaming, NetEnt, and Play’n GO. Reputable online casinos work with licensed developers. Pay attention to:
- Number of available slots.
- Quality of the live casino section.
- Variety of table games.
- Availability of crash games and other innovations.
- Bonuses and Promotions
Read bonus terms and conditions carefully:
- Wagering Requirements (wagering) – prefer casinos with a WR below 40x.
- Bonus redemption time limits.
- Bonus exclusions.
- Maximum stakes when playing with a bonus.
- Maximum bonus payout.
- Payment Methods
Choose a European casino that accepts methods convenient for you:
- BLIK for Polish players.
- Visa and Mastercard.
- E-wallets (Skrill, Neteller, MiFinity).
- Cryptocurrencies for anonymity and fast transactions.
Check deposit and withdrawal limits and transaction processing times.
- Customer Service
Prefer casinos with:
- Polish-language support.
- 24/7 live chat.
- Fast response times.
- Professional consultants.
- Player Reviews
Read reviews and opinions from other players on independent forums such as Trustpilot, AskGamblers, or CasinoMeister. Pay attention to reviews about:
- Payout speeds.
- Customer service quality.
- Gaming integrity.
- Verification process.
- Responsible gaming tools
Check the availability of:
- Deposit limits.
- Time limits.
- Self-exclusion options.
- Links to aid organizations.
- Withdrawal times and limits
Prefer foreign casinos with:
- Fast withdrawals (0-24 hours).
- High daily and monthly limits.
- No hidden fees.
- Weekend withdrawals.
Play Responsibly – Safe Gaming Rules
Online gambling should be a form of entertainment, not a way to make money. Remember the principles of responsible gaming.
Basic Rules
18+ Only for Adults – Casino gaming is only permitted for individuals 18 years of age or older.
Set Financial Limits – Before playing, determine exactly how much money you can spend on entertainment. Never gamble with money intended for bills, food, or other essential expenses.
Set Time Limits – Determine how much time you can spend in the casino and stick to it. Use the session limits available in casinos.
Don’t Play Under the Influence – Avoid playing under the influence of alcohol, drugs, or strong emotions. Psychoactive substances and emotions impair judgment and lead to irrational decisions.