Interview Questions for Understanding of Paper and Ink

Paper fibers are the fundamental building blocks of paper, significantly influencing print quality. The primary types are wood fibers (softwood and hardwood), and cotton or linen fibers (for specialty papers). Softwood fibers, like those from pine or spruce, are long and flexible, creating a paper that’s strong but can be slightly rougher. This roughness can affect ink absorption and potentially lead to less crisp print detail, especially with fine lines or small text. Hardwood fibers, from deciduous trees like birch or maple, are shorter and create a smoother, denser sheet of paper, generally resulting in superior print quality, particularly for high-resolution images and detailed text. Cotton and linen fibers, found in high-quality papers like watercolour paper, offer exceptional strength, smoothness, and absorbency, ideal for techniques requiring high ink loads or specialized printing methods like screen printing. The blend of fiber types dictates the final paper characteristics.

• Softwood fibers: Stronger, more absorbent, rougher surface, suitable for less demanding printing.
• Hardwood fibers: Smoother surface, better ink holdout (less ink absorption), higher print quality.
• Cotton/Linen fibers: Exceptional strength, smoothness, absorbency, used for high-end papers.

Paper finishes significantly impact print quality and aesthetics. They’re created during the paper manufacturing process by applying coatings or through variations in the paper’s calendering (pressing).

• Coated paper: Has a smooth, clay-coated surface that provides excellent ink holdout, vibrant colors, and sharp details. Common types include gloss, matte, and dull coated. Gloss offers the highest sheen and vibrant colors, matte is less shiny and reduces glare, while dull coated provides a balance between the two. Coated paper is ideal for high-quality magazines, brochures, and packaging where image quality is paramount.
• Uncoated paper: Has a natural, porous surface with little to no coating. Ink is absorbed into the paper, resulting in a less vibrant appearance but with a more textured feel. Uncoated paper is common for office printing, books, and stationery. Sub-categories include offset, text, and bond papers, each with slightly different properties and uses. Offset is used for high-volume printing, text for general purposes, and bond for writing and stationery.

The choice of finish depends on the intended application and the desired aesthetic. For instance, a glossy finish works well for eye-catching advertisements, while a matte finish is preferred for documents that require less glare.

Paper grammage, expressed in grams per square meter (gsm), refers to the paper’s weight and thickness. It directly impacts printability. Higher gsm papers are thicker and stronger, offering better dimensional stability and preventing ink from showing through (show-through). This is beneficial for duplex printing (printing on both sides). However, heavier papers may require specialized printing presses and can be more expensive. Lower gsm papers are lighter and less expensive, but they may be more prone to wrinkles, show-through, and can be less durable. The choice of grammage is influenced by the printing method, the desired print quality, and the budget.

For example, a lightweight 80gsm paper might be suitable for leaflets or low-quality printing, while a heavier 250gsm paper might be better suited for business cards or postcards.

Solvent-based and water-based inks differ significantly in their composition, properties, and environmental impact.

• Solvent-based inks: Use organic solvents as their primary carrier. They offer excellent vibrancy, quick drying, and good adhesion to various substrates. However, they are more volatile, produce strong odors, and pose greater environmental concerns due to the volatile organic compounds (VOCs). They are commonly used in flexographic and screen printing.
• Water-based inks: Employ water as the primary carrier. They are less volatile, have minimal odor, and are considered more environmentally friendly. However, they generally dry slower than solvent-based inks and may not offer the same level of vibrancy or adhesion in certain applications. They are increasingly favored in offset and digital printing, especially where environmental regulations are stringent.

The choice depends on factors like environmental regulations, the substrate being printed, the required drying time, and the print quality expectations. Water-based inks are a greener option but might not always deliver the same level of brilliance.

Ink pigments are the finely ground color particles in ink. They are crucial for color reproduction. Different pigments offer unique characteristics in terms of color, opacity, lightfastness (resistance to fading), and chemical stability. Pigments can be organic (derived from natural sources or chemical synthesis) or inorganic (mineral-based).

• Organic pigments: Often offer a wider range of bright, vibrant colors but can be less lightfast than inorganic pigments.
• Inorganic pigments: Generally exhibit better lightfastness and opacity, but the color range might be more limited.

For instance, azo pigments are common organic pigments known for their bright hues, while titanium dioxide is an inorganic pigment used for its high opacity (whiteness) and commonly used in white inks or to increase the opacity of other colors. The careful selection of pigments is essential for achieving accurate color reproduction and maintaining the longevity of the print.

Color gamut refers to the entire range of colors that a particular printing system can reproduce. It’s a crucial aspect of ink selection. Each ink set has a specific color gamut, determined by the available pigments and the printing process. The wider the gamut, the more colors the system can accurately reproduce.

The choice of ink directly impacts the achievable color gamut. For instance, a CMYK (cyan, magenta, yellow, black) ink set, common in offset printing, has a limited gamut compared to a wider gamut achieved using extended color gamut inks (e.g., adding orange, green, or violet inks). Pantone Matching System (PMS) inks offer a very wide gamut and the ability to reproduce specific named colours accurately, but are more expensive and not suitable for high-volume printing. The selection of inks, therefore, depends on the required color accuracy and the printing budget. Matching the desired color gamut to the printing process’s capabilities is essential for accurate color reproduction.

Ink drying is a complex process influenced by the ink type, paper properties, and environmental conditions (temperature, humidity). It impacts print durability.

• Solvent-based inks: Dry primarily through solvent evaporation. The speed of drying depends on the solvent’s volatility and the surrounding air’s temperature and humidity. Faster drying can sometimes lead to reduced color vibrancy, while slower drying can result in smudging.
• Water-based inks: Dry mainly through water absorption into the paper and subsequent water evaporation. The drying process is significantly influenced by the paper’s absorbency. High-absorbency paper will lead to faster drying but might increase the risk of feathering (ink bleeding).

Proper ink drying is crucial for print durability. Insufficient drying can lead to smudging, sticking, and color bleeding. Excessive drying can cause cracking or flaking of the ink layer, particularly on uncoated paper. Understanding and controlling the ink drying process is paramount to achieving prints with long-lasting color and sharpness.

Paper defects can significantly hinder the printing process and final product quality. Common defects include:

• Holes and pinholes: Tiny holes that can cause ink bleed or show through to the other side of the paper.
• Wrinkles and creases: These distort the printed image and can make the paper difficult to handle.
• Stains and discolorations: Uneven coloring of the paper affects the uniformity of the printed colors.
• Calendering marks: These are shiny or dull streaks caused by uneven pressure during the paper manufacturing process. They can create inconsistencies in ink absorption.
• Moisture content variations: Uneven moisture leads to dimensional instability, causing problems like curling, jamming, and misregistration in printing.
• Broken fibers: Weak fibers can cause the paper to tear during printing or handling.

The impact on printing depends on the severity and type of defect. For instance, small pinholes might be unnoticed in a newspaper, but they would be unacceptable in high-quality photographic prints. Wrinkles will cause distortion regardless of print type. Ultimately, paper defects lead to waste, increased printing costs, and a reduction in the overall quality of the final product. A print shop might need to reject a whole batch of paper if defects are widespread.

Color management is the process of controlling the colors throughout the printing workflow, from design to final output. It ensures that the colors seen on a screen accurately reflect the colors printed on the paper. This is crucial because different devices (monitors, printers) use different color models and have varying color gamuts (the range of colors they can reproduce).

Imagine trying to paint a portrait using only a limited set of colors – you wouldn’t be able to accurately reproduce all the nuances of skin tone. Similarly, without proper color management, your printed image may look dull, washed-out, or completely different from your digital design. Color management involves using color profiles (like ICC profiles) that define the color characteristics of each device. These profiles help translate colors between devices, ensuring consistency. For example, a printer profile will tell the printer how to mix inks to achieve a specific color based on its capabilities. Without it, the printer would simply guess, resulting in unpredictable and inaccurate color reproduction.

Poor color management leads to costly reprints and client dissatisfaction. Accurate color reproduction is essential for brands to maintain consistency across marketing materials, packaging, and other printed products.

There are many printing processes, but three common ones are:

• Offset Printing: This is a high-volume, cost-effective process using plates to transfer ink onto a rubber blanket, and then onto the paper. It’s ideal for large print runs, like books, magazines, and brochures, providing excellent image quality and consistent color reproduction.
• Digital Printing: This method prints directly from a digital file onto the paper, making it suitable for short runs, personalized prints, and on-demand printing. It’s faster and more flexible than offset but might be more expensive per unit for large quantities. Examples include business cards, flyers, and custom-designed stationery.
• Flexographic Printing: This process uses flexible relief plates and is commonly used for packaging, labels, and flexible materials. It’s known for its high speed and ability to print on a wide range of substrates, including plastic films and corrugated cardboard. The ink is applied to the plate with a roller and transferred to the substrate.

Each process has its own strengths and weaknesses regarding cost, speed, quality, and suitability for different applications. The choice depends on the project’s requirements – print volume, desired quality, budget, and substrate.

The choice of substrate (the material being printed on, usually paper) significantly impacts the printing process and the final result. Different papers have varying properties that affect ink absorption, smoothness, and overall print quality.

• Porosity: Highly porous papers (like newsprint) absorb ink quickly, potentially leading to feathering or bleeding, but providing lower cost. Less porous papers (like coated stock) provide sharper images and crisper text.
• Surface finish: Coated papers generally offer better image quality and smoother printing surfaces compared to uncoated papers. The type of coating (matte, gloss, etc.) also influences the final look and feel.
• Weight and thickness: Heavier papers are more durable but can be more challenging to feed through certain printing machines. They often provide a more luxurious feel.
• Brightness and color: The paper’s natural brightness and color can affect the perceived color of the printed image. For example, using a yellowish paper with cyan ink will produce a slightly greener result.

For example, printing a high-resolution photograph on cheap, porous paper will result in a blurry and faded image. Using the same photograph on a high-quality coated paper will showcase its detail and vibrancy. Choosing the appropriate substrate is critical for achieving the desired outcome.

Ink viscosity, or thickness, is a critical factor influencing print quality. It determines how easily the ink flows, transfers, and dries. Too high a viscosity results in poor ink transfer, leading to light, uneven prints, and potentially clogging the print heads. Too low a viscosity can lead to excessive ink spread, blurring, and feathering.

Think of painting with different types of paint – thick oil paint doesn’t spread easily and requires more effort, while thin watercolor spreads quickly and requires careful control. Similarly, in printing, the ideal viscosity depends on the printing process and the substrate. Offset printing typically requires lower viscosity inks than screen printing. The viscosity is often adjusted by adding reducers or thickeners depending on environmental conditions (temperature and humidity).

Maintaining the correct ink viscosity is essential for consistent color reproduction, sharp image detail, and preventing defects like mottle (uneven ink distribution).

Environmental concerns are increasingly important in paper and ink selection. Sustainable practices focus on reducing the environmental impact at every stage of the production and disposal processes.

• Paper sourcing: Choosing paper from responsibly managed forests (certified by organizations like the Forest Stewardship Council – FSC) ensures that paper production doesn’t contribute to deforestation.
• Recycled content: Using paper with high recycled content reduces the demand for virgin pulp, conserving natural resources and lowering energy consumption.
• Ink formulations: Selecting inks with low volatile organic compounds (VOCs) minimizes air pollution and contributes to better indoor air quality. Vegetable-based inks are a more environmentally friendly option compared to petroleum-based inks.
• Waste management: Implementing efficient waste management strategies, including recycling paper and ink cartridges, reduces landfill waste.
• Energy consumption: Choosing printing processes and materials that require less energy reduces the carbon footprint of the printing operation.

Many organizations and customers prioritize eco-friendly printing practices. By selecting sustainable papers and inks, businesses can demonstrate their commitment to environmental responsibility and attract environmentally conscious clients.

Paper coatings modify the paper’s surface properties, impacting printability, appearance, and durability. Common types include:

• Clay coatings: These are the most common type, providing a smooth, even surface for high-quality printing, especially for offset printing. They increase opacity and brightness.
• Calcium carbonate coatings: Similar to clay coatings, but often less expensive and can provide good brightness and opacity.
• Polymer coatings: These coatings, often made from synthetic polymers, provide excellent water resistance, scratch resistance, and gloss. They are frequently used in high-end magazines and packaging.
• UV coatings: These coatings are applied after printing and cured with ultraviolet (UV) light. They offer superior protection against scuffs and scratches, enhancing the durability and visual appeal of the printed product. Gloss UV coatings add shine, while matte UV coatings provide a more subtle finish.

The choice of coating depends on the desired print quality, application, and budget. For instance, a glossy coating enhances the vibrancy of images, while a matte coating might be preferred for text-heavy documents to reduce glare. Coated papers are generally more expensive than uncoated papers but provide significantly better printing results for many applications.

Maintaining color consistency across print runs is crucial for brand identity and product quality. It requires a multi-faceted approach focusing on standardized processes and careful material management.

• Color Profile Management: Using a standardized color profile (like ICC profiles) ensures that the color data sent to the printer accurately represents the intended color. This profile acts as a translator between the digital file and the printing process.

• Ink Consistency: Maintaining consistent ink viscosity and density is paramount. Regular monitoring of ink levels and mixing is essential. We often use spectrophotometers to measure and adjust ink density for precision.

• Calibration and Maintenance: Regular calibration of printing equipment – including colorimeters and spectrophotometers – ensures consistent output. Preventive maintenance of the printing press, such as cleaning print heads and replacing worn parts, also contributes to stable color reproduction.

• Paper Consistency: Variations in paper stock (even slight ones in brightness, absorbency, and smoothness) can affect color appearance. We utilize paper from the same batch or lot number across print runs, and sample testing is conducted before production to check consistency.

• Control Strips and Proofing: Printing control strips (color bars) on each sheet allows monitoring color consistency throughout the run. Proofing – generating a sample print before the main run – allows for final color adjustments and verification.

For example, imagine printing a corporate brochure. Inconsistent colors across different print runs would damage brand perception and hurt the client’s trust. The above steps are critical to avoid this.

Troubleshooting printing problems requires a systematic approach, isolating the issue to either the paper, the ink, or the printer itself.

• Paper-related issues: Problems like paper jams, misfeeds, or uneven print quality (e.g., streaks, blotches) often stem from issues like incorrect paper type, humidity affecting the paper’s moisture content, or damaged paper. Solutions range from using the correct paper specifications for the printing press to adjusting environmental conditions and checking for physical damage in the paper stock.

• Ink-related issues: Clogged print heads, incorrect ink viscosity, or incorrect ink mixing can lead to faded colors, banding, or other print defects. Cleaning the print heads, checking the ink density using a spectrophotometer, and ensuring proper ink mixing are essential troubleshooting steps.

• Printer-related issues: Malfunctioning print heads, incorrect printer settings (like resolution or color profiles), or other mechanical issues can also affect print quality. Careful inspection of the printer, adjustments to settings, and sometimes professional maintenance are necessary.

Imagine a client complaining about faded colors on a poster print. We would systematically investigate if this was due to ink issues (low ink density, clogged nozzles), paper issues (excessive ink absorption), or printer issues (incorrect color settings). This structured approach is key to effective troubleshooting.

Quality control for paper and ink is crucial for consistent and high-quality printing. This involves both incoming inspection and ongoing monitoring.

• Paper Quality Control: We assess factors like brightness, opacity, thickness, smoothness, grammage, and moisture content. Instruments like brightness meters and caliper gauges are utilized. We also test for defects like pinholes or inconsistencies in thickness.

• Ink Quality Control: For inks, we inspect color consistency, viscosity, and density. Spectrophotometers accurately measure color values ensuring they meet predetermined standards. We also check for proper chemical composition and stability.

• Random Sampling: Both paper and ink undergo random sampling from each batch or shipment to ensure the quality of the entire lot. This is a statistical method that provides confidence in the quality of the supply.

• Documentation and Traceability: Detailed records, including supplier certifications and test results, are meticulously maintained for traceability. This enables identification of the source of any problems and prevents their recurrence.

For example, failing to test paper for moisture content might lead to paper buckling during printing, ruining a large print run. Our rigorous quality control measures help us prevent this.

Paper porosity and ink absorption are directly related. Porosity refers to the level of interconnected spaces within the paper structure. The more porous the paper, the more easily ink will be absorbed.

High porosity paper, like newsprint, readily absorbs ink, leading to quicker drying times but potentially lower image sharpness. Low porosity paper, like coated paper, absorbs ink more slowly, resulting in sharper images and richer colors but often requiring more drying time. The relationship is crucial in choosing the appropriate paper for a specific printing technique and desired result.

Imagine printing a fine-art photograph. A high-porosity paper would lead to a muddy and less defined image. In contrast, a low-porosity, coated paper ensures precise ink placement and vivid colors, showcasing the photograph’s details.

Dot gain refers to the enlargement of printed dots of ink during the printing process. Ideally, a printed dot should be the same size as the dot created by the printing plate or screen. However, due to factors like ink spread and paper absorption, the printed dot is usually larger.

Excessive dot gain can lead to darker images and a loss of detail, affecting image sharpness and contrast. Conversely, insufficient dot gain can result in images appearing too light. Controlling dot gain is crucial for achieving accurate color reproduction and image quality. Factors that influence dot gain include the type of paper, ink, printing press, and printing conditions.

For example, printing vibrant halftones (gradual transitions between colors) requires careful control of dot gain to prevent the colors from appearing muddy or dark. Accurate dot gain is crucial for color accuracy.

Maintaining accurate ink densities is vital for consistent color reproduction and overall print quality. Ink density refers to the concentration of ink in a printed area. It directly affects the color’s appearance, vibrancy, and saturation.

Inconsistent ink densities lead to uneven color throughout the print, faded or overly saturated areas, and color mismatches compared to the original design. Precise ink densities are crucial for matching specific color standards, reproducing consistent brand colors, and achieving accurate color reproduction across different print runs.

Imagine printing a food packaging label with specific Pantone color codes. Inaccurate ink densities would lead to a color mismatch, potentially failing quality control and harming brand recognition. Consistent ink density is imperative for color accuracy.

Paper’s moisture content significantly impacts printing. The ideal moisture content varies depending on the paper type and printing process, but significant deviations can cause problems.

High moisture content can lead to paper stretching, causing misregistration (where colors don’t align properly), and increased ink absorption leading to blurry images and slower drying times. Low moisture content can lead to static electricity, paper jams, and increased susceptibility to wrinkling or cracking during printing. This underscores the importance of storing paper in appropriate environmental conditions.

For example, printing on paper that’s too dry can result in a static discharge that attracts dust particles, creating specks or blemishes on the print. Conversely, printing on excessively damp paper might cause the ink to bleed, blurring the image.

Ink drying methods significantly impact print quality and longevity. Different methods offer various advantages and disadvantages depending on the application and ink type.

• Absorption: This method relies on the paper absorbing the ink. It’s simple and cost-effective, often used with porous papers and dye-based inks. However, it can lead to slower drying times and potential smudging. Example: Newspaper printing uses absorption primarily.
• Oxidation: This method uses oxygen to polymerize the ink, forming a solid film. It’s faster than absorption and produces more durable prints, commonly used with oil-based inks. However, it can be sensitive to humidity and may require specific ink formulations. Example: Many high-quality art prints employ oxidation drying.
• Evaporation: This involves the solvent in the ink evaporating, leaving behind a pigmented film. This is common with solvent-based inks used in screen printing and some inkjet technologies. It’s fast but can have environmental concerns related to volatile organic compounds (VOCs). Example: Solvent-based inks for signage often rely on evaporation.
• UV Curing: This utilizes ultraviolet light to instantly cure the ink, offering exceptionally fast drying and high durability. It’s prevalent in large-format printing and specialized applications. However, the equipment cost is significant. Example: Wide-format advertising banners often use UV curing.

The choice depends on factors such as speed, cost, environmental impact, print quality requirements, and the type of paper and ink used.

Color calibration and profiling are crucial for achieving accurate and consistent color reproduction. My experience encompasses both hardware and software aspects. I’ve extensively used colorimeters and spectrophotometers to measure the color output of various printers and inks, then used profiling software to generate ICC profiles (International Color Consortium profiles). These profiles act as translators, ensuring the printer accurately renders colors based on industry standards. I’ve worked with various color spaces, including sRGB, Adobe RGB, and Pantone, adapting profiles based on specific project needs and paper types. For example, I once helped a client accurately reproduce their corporate branding colors on a new line of packaging, requiring meticulous profiling to ensure consistency across different printing runs.

Troubleshooting inconsistencies is a key aspect of my work, involving analysis of paper properties, ink formulation, and printer settings to identify and rectify discrepancies. It’s not just about matching colors on a screen; it’s about understanding the physical limitations of ink and paper in order to reach the desired result.

Ink smearing and feathering are common print defects stemming from poor paper selection or ink incompatibility. Addressing these issues requires a systematic approach.

• Identify the Cause: First, determine if the problem is caused by excessive ink absorption (feathering) or insufficient drying (smearing). A simple test is to observe whether ink spreads from the printed area.
• Paper Selection: Using paper with appropriate sizing (a treatment to reduce ink absorption) is crucial. Coated papers usually offer superior resistance to feathering. Smooth paper surfaces also reduce smearing.
• Ink Adjustments: If the ink is too wet, try reducing the ink concentration or switching to a faster-drying ink. For inkjet printers, adjusting print settings like drying time might be necessary.
• Environmental Factors: High humidity can exacerbate smearing. Controlling the ambient environment, including temperature and humidity, can prevent issues.
• Post-Print Treatment: In some cases, applying a protective coating after printing can prevent smearing or smudging.

Often, a combination of these methods might be required. A methodical investigation is key to pinpoint the cause and implement a proper fix.

Testing paper strength and durability ensures that the paper meets the requirements of its intended application. Several methods exist:

• Tensile Strength: This measures the force required to break a paper strip, indicating its resistance to tearing. A tensile strength tester is used, pulling the paper sample until it breaks.
• Burst Strength: This indicates the paper’s resistance to internal pressure, crucial for applications like packaging. A burst tester applies increasing pressure until the paper ruptures.
• Tear Strength: This measures the force needed to tear a paper sample, assessing its resistance to tearing. A tear strength tester simulates a tearing motion.
• Folding Endurance: This tests the number of folds a paper sample can withstand before breaking, providing information about its flexibility and durability. A folding endurance tester automatically folds the paper sample until failure.
• Mullen Burst Test: A specific type of burst test often used in the paper and packaging industries.

The choice of test depends on the specific application. For example, packaging materials require high burst and tensile strengths, while fine art paper might prioritize folding endurance and tear resistance.

Paper recycling is vital for environmental sustainability, reducing reliance on virgin timber and minimizing landfill waste. The process involves collecting used paper, pulping it (breaking down the fibers), cleaning the pulp, and then reforming it into new paper.

However, not all paper is equally recyclable. Contaminants like plastic coatings, adhesives, or inks can hinder the recycling process. The quality of recycled paper is generally lower than virgin paper due to fiber degradation during the recycling process. The environmental impact is complex. While recycling reduces deforestation and landfill waste, the energy required for pulping and processing can still contribute to greenhouse gas emissions. Furthermore, some inks and coatings contain substances that are harmful to the environment. The ideal scenario involves minimizing waste, using recycled paper whenever possible, and supporting responsible forestry practices to ensure a balanced and sustainable approach.

Selecting the right paper and ink for a specific application involves considering several factors:

• Intended Use: Is it for a high-quality art print, a business document, or packaging? Different applications have different durability, aesthetic, and functional requirements.
• Paper Properties: Weight, texture, surface finish (coated, uncoated), opacity, and brightness all affect the final print quality. Coated papers provide smoother surfaces for sharp images, while uncoated papers offer a more natural texture.
• Ink Type: Different inks (dye-based, pigment-based, solvent-based, UV-curable) have varying properties such as color vibrancy, durability, and drying times. Dye-based inks are often more vibrant but less water-resistant, while pigment-based inks are more durable but may be slightly less vivid.
• Print Method: The printing method (offset, inkjet, screen printing) dictates the suitable paper and ink combinations.
• Budget: Costs vary significantly based on paper quality and ink type.

The process is iterative. Testing and experimentation often are needed to find the optimal combination that meets the project’s specifications.

My experience includes using a range of paper testing equipment, both basic and sophisticated. This includes:

• Paper Thickness Gauge: Measures the thickness of paper samples to ensure consistency.
• Caliper Gauge: Similar to a thickness gauge, but can be more precise.
• Moisture Meter: Determines the moisture content of paper, essential for consistent printing and paper handling.
• Brightness Meter: Measures the brightness of paper, important for color reproduction.
• Opacity Meter: Measures the ability of paper to block light, crucial for preventing show-through of print on the reverse side.
• Tensile Strength Tester, Burst Strength Tester, Tear Strength Tester, Folding Endurance Tester: These sophisticated instruments measure various strength parameters as described earlier.
• Spectrophotometer: Measures the color of paper samples for accurate color management.

Understanding the capabilities and limitations of each device is critical for accurate and reliable testing, leading to the right paper selection for the task.