Fountain Solution Testing in Offset Printing: Using a Refractometer to Check Concentration

A practical guide to fountain solution mixing, pH, conductivity, refractive index and water quality

Fountain solution is one of the most important fluids in offset lithographic printing. Its chemistry helps keep non-image areas of the printing plate receptive to water and resistant to ink. When the solution is incorrectly mixed, contaminated or poorly maintained, printers can experience toning, scumming, unstable ink-water balance, plate problems and unnecessary production waste.

For print shops, controlling fountain solution means understanding three important measurements: pH, electrical conductivity and refractive index. Each provides different information. Used together appropriately, they can help operators establish a consistent fresh mixture and identify changes during production.

A BOSS Refractometer can be useful when checking the concentration of a freshly prepared fountain solution, provided the instrument’s reading has been correlated with the particular concentrate being used.

What Is Fountain Solution?

Fountain solution, also called dampening solution, is the water-based fluid used in offset lithography. It forms a controlled film on the non-image areas of the printing plate, helping prevent those areas from accepting ink.

The working solution generally consists of water mixed with a formulated fountain solution concentrate. Depending on the printing process and product, an additional alcohol substitute or isopropyl alcohol (IPA) may also be used.

Concentrates can contain several functional ingredients, including:

• Buffers: Help stabilize pH.
• Wetting agents: Help the solution spread across the plate.
• Plate-protecting ingredients: Help maintain the desired condition of non-image areas.
• Corrosion inhibitors and other additives: Support compatibility with the press and its operating conditions.

The exact formulation varies by manufacturer and product. That variation matters because different fountain concentrates can produce different pH, conductivity and refractive-index readings at the same dilution percentage.

How Is Fountain Solution Mixed?

Many commercial printing operations use automatic proportioning or dosing equipment. These systems meter concentrate into water at a specified ratio, reducing the variability associated with manual mixing. Smaller operations may prepare batches manually or use simpler dosing arrangements.

Some presses use a one-step fountain concentrate. Other systems use a two-step approach in which fountain concentrate and an alcohol substitute are added separately.

The working solution is commonly held in a reservoir and circulated through the press. Refrigeration may be used to maintain the temperature required by the specific process.

Mixing instructions must come from the concentrate manufacturer. A product might call for a particular number of ounces per gallon, a percentage by volume or another specified dosage. There is no universal mixing ratio suitable for every fountain solution.

Why Check a Fresh Mixture?

Even when dosing equipment is installed, verifying a fresh batch can help identify incorrect settings, dosing errors or changes in the source water.

A useful starting procedure is to record the water’s baseline measurements, prepare the solution according to the product instructions, and measure the fresh mixture. Those readings become a reference for that particular water-and-concentrate combination.

The Three Main Measurements

1. pH: Measuring Acidity and Alkalinity

pH describes the acidity or alkalinity of a solution. Fountain concentrates are formulated to operate within product-specific pH conditions.

A pH meter can help identify a fresh mixture that falls outside its intended range. It can also reveal changes that might not be apparent from conductivity alone.

However, pH is not a direct measurement of concentrate concentration. Because fountain solutions contain buffering ingredients, pH may remain relatively stable even when the amount of concentrate changes.

Use pH to monitor the solution’s acid-base condition, not as a stand-alone dilution measurement.

2. Conductivity: Monitoring Dissolved Ions

Electrical conductivity measures a solution’s ability to carry electrical current. It is commonly expressed in microsiemens per centimeter (µS/cm).

As an ionic fountain concentrate is added to water, conductivity generally increases. This makes conductivity a widely used method for checking fresh mixtures and monitoring operating fountain solution.

However, conductivity is not a direct measurement of total dissolved solids, nor does it identify individual chemicals. Its relationship to concentrate dosage depends on the concentrate’s formulation and the water being used.

Other dissolved substances can affect the reading. Paper-coating minerals, ink components, wash chemicals and other contaminants may change conductivity during production. Temperature also affects the measurement.

For that reason, operators should establish a product-specific baseline rather than assume one universal conductivity target applies to every fountain solution.

3. Refractometry: Measuring the Effect on Light

A refractometer measures how light bends as it passes through a liquid. This property is called refractive index.

Many handheld refractometers display the measurement as a Brix value. Brix is defined using sucrose solutions, so a Brix reading from a fountain solution does not mean that the liquid contains that percentage of sugar.

Instead, the displayed value can serve as a comparative concentration indicator when the instrument has been checked against known dilutions of the specific product.

For example, a printer could prepare several fresh samples at known concentrate dosages and measure each sample with the same refractometer. If the readings change consistently with concentration, the printer can develop a reference chart for that product and water source.

This is the basis for using a BOSS Refractometer to check a freshly mixed solution. The relationship must be established experimentally rather than assumed from the Brix scale alone.

How to Use a BOSS Refractometer for Fresh Fountain Solution

The following procedure is intended to establish a product-specific reference. Follow the instrument instructions and the fountain concentrate manufacturer’s safety and handling guidance.

Step 1: Identify the concentrate.

Record the manufacturer, exact product name and recommended working dilution. Do not assume that two concentrates from different suppliers will produce the same reading at the same dosage.

Step 2: Establish a water baseline.

Measure the water that will be used to prepare the mixture. Record its refractometer reading and, where appropriate, its conductivity and pH.

Water sources can differ in dissolved minerals and other constituents. Changes in water quality can affect the results.

Step 3: Prepare known dilutions.

Prepare several fresh samples at accurately measured concentrations spanning the manufacturer’s recommended working range. Use a consistent dilution convention and suitable measuring equipment.

Step 4: Measure each sample consistently.

Clean the prism between samples. Follow the refractometer’s temperature and calibration instructions, and allow samples to reach an appropriate, consistent measurement temperature.

Record the reading for every known dilution.

Step 5: Create a reference chart.

Plot the refractometer reading against the known concentration. If the readings are repeatable and sufficiently separated to distinguish the relevant concentrations, the chart may be useful for routine fresh-mix checks.

Step 6: Revalidate when conditions change.

Recheck the relationship if the concentrate batch, water source, formulation or measurement conditions change. A chart developed for one product should not automatically be applied to another.

The instrument’s resolution and repeatability must also be adequate for the concentration differences the operator needs to detect.

Why Refractometer Readings Can Mislead in Used Fountain Solution

Freshly mixed solution and solution that has circulated through a printing press are not necessarily equivalent samples.

During production, the working fluid may pick up material from paper coatings, ink, cleaning agents and other sources. These substances can change refractive index independently of the original concentrate dosage.

Temperature changes can also affect refractive-index measurements.

Prisco’s technical bulletin specifically cautions that refractometer readings can be unreliable for accurately controlling fountain concentrate and alcohol-substitute dosage over time. It limits their use to controlled circumstances involving fresh mixed solution or separately metered alcohol substitute, with consistent measurement conditions.

For this reason, a BOSS Refractometer should not be presented as a universal test for determining whether a used fountain-solution tank is still fit for service.

For in-service monitoring, use the measurements and maintenance procedures recommended by the fountain solution supplier and press manufacturer. Conductivity and pH remain important tools, but neither should be interpreted without considering the product, water, temperature and possible contamination.

What About Water Quality?

Water is a major part of fountain solution, and its composition can affect press performance.

Hardness, alkalinity and dissolved minerals may influence the behavior of the concentrate. Inconsistent source water can also make measurements less consistent from one batch to another.

Some print shops use reverse-osmosis treatment or other water-treatment systems to achieve more consistent water quality. The appropriate approach depends on the incoming water and the requirements of the fountain solution.

It is not accurate to assume that every shop must use reverse-osmosis water or that deionized water is always unsuitable. Water treatment should be selected according to the concentrate manufacturer’s instructions and the pressroom’s technical requirements.

When investigating inconsistent readings, record the water source and its baseline properties before changing the concentrate dosage.

When Should Fountain Solution Be Replaced?

There is no single replacement interval that applies to every pressroom.

The decision depends on the product, the circulation system, operating conditions, contamination, maintenance practices and the manufacturer’s recommendations.

Operators may replenish water or solution lost during operation, correct a verified dosing problem, or drain and replace the working solution when its condition or the supplier’s maintenance schedule requires it.

A refractometer reading alone cannot establish that used solution is clean, chemically balanced or suitable for continued service. A reading that appears normal does not rule out contamination.

Keep records of fresh-mixture measurements and compare them with readings taken during operation and at solution replacement. Those records help establish the normal operating range for the particular press and product.

Frequently Asked Questions

Can a BOSS Refractometer measure fountain solution concentration?

It may be used to estimate the concentration of a particular fresh fountain solution if known dilutions establish a repeatable relationship between the reading and dosage. Suitability depends on the product’s formulation and the refractometer’s resolution and repeatability.

Does a Brix reading represent the percentage of fountain concentrate?

Not automatically. Brix is a sucrose-based scale. For fountain solution, it is only a comparative indicator unless the reading has been calibrated against known concentrations of the specific formulation.

Can I use the same calibration chart for different fountain concentrates?

No. Different formulations can produce different refractive-index responses at the same dosage. Prepare a separate chart for each product and verify it when relevant conditions change.

Can a refractometer replace a conductivity meter?

Not for every task. A refractometer can help check a fresh mixture under controlled conditions. Conductivity is widely used for monitoring fountain solution during production, although contamination and changes in water quality can affect its readings.

Can I test used fountain solution with a refractometer?

You can obtain a reading, but it may not reliably indicate concentrate concentration because contaminants can change refractive index. Follow the supplier’s procedures for evaluating used solution.

Do I still need a pH meter?

A refractometer does not measure pH. If pH monitoring is required for the product and press, use an appropriate pH meter and follow the manufacturer’s measurement and calibration guidance.

A Practical Approach to Fountain Solution Control

Reliable fountain solution control begins with consistent mixing, known water quality, product-specific reference measurements and regular monitoring.

A BOSS Refractometer may provide a convenient additional check when preparing fresh fountain solution, particularly where a printer wants to verify that a known dilution produces a consistent reading. Its usefulness should be established with the actual concentrate being used.

For routine production control, continue to follow the fountain solution supplier’s recommendations for pH, conductivity, temperature, contamination and replacement.

The goal is not to rely on one number. It is to establish a repeatable process that helps keep fountain solution within the operating conditions required by the press.

Technical references

• Prisco, TechSolutions 19: Pocket Digital Refractometer. Discusses the limitations of refractometry for fountain concentrates, alcohol substitutes and used mixed solutions: https://prisco.com/wp-content/uploads/2018/03/TechSolutions-19.pdf
• Printing Industries of America, Should I Measure the pH or Conductivity of My Fountain Solution?: https://www.printing.org/content/2018/03/28/should-i-measure-the-ph-or-conductivity-of-my-fountain-solution
• Flint Group, Varn Supreme 8100 Technical Data: https://www.flintgrp.com/media/t4lfb3t5/varn_supreme8100_sf_pmna.pdf
• Verso, Technical Bulletin: Fountain Solutions, pH and Conductivity: https://www.versoco.com/ww/wcm/connect/953f3316-ec33-4699-b997-3ac36f1933ad/Technical%2BBulletin%2BFountain%2BSolutions.pdf?MOD=AJPERES

Always consult the current technical data sheet for the exact fountain solution in use. Product formulations, recommended dilution rates and operating targets vary.