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Enamels Troubleshooting Guide

PROBLEM   CAUSES   SOLUTIONS
Poor Adhesion A. Underfired. A. Increase temperature and/or slow down speed through firing cycle.
  B. Contaminated substrate. B. Clean or prefire substrate.
Alligatoring A. Overprint is higher melting and/or more viscous during firing operation than undercoat. A. Obtain higher melting undercoat or lower melting overcoat from supplier.
Also: Tearing, Cracking
 
  B. In UV systems this is often due to the wet film thickness being too thick. B. Reduce wet film thickness.
Backlap A. Too much coating on the screen. A. Reduce volume of coating material.
Also:
Backlash
Belt marks   See Chain marks.    
Blister A. Moisture A.  
(1) Condensation caused by substrate being brought into warm room after being stored in cool area. (1) Bring substrate into printing and/or firing area 24 hours prior to processing.
(2) Condensation under print caused by screening on cold substrate. (2) Same as A (1).
(3) Moisture in the color itself caused either by leaving containers open for excessive periods of time or moisture in the powder prior to being mixed with oil. (3) Keep container tightly sealed when not in use. Consult supplier if problem persists.
  B. Carbonaceous Materials B.  
(1) Resins or other ingredients in the oil (or additives) that leave a residue (ash) upon firing. Usually gives the color a grayish cast. (1) Keep records of additives and quantities. Consult supplier if problem persists.
(2) Excessive furnace heat combined with low melting ceramic coating which causes the surface film of the enamel to fuse before the organic materials (oils, thickeners, etc.) are completely burned out. (2) Preheat to 800F (427C) for 4 to 6 minutes. May need to change vehicle (medium) or use higher firing ceramic. Lower temperature a entrance of furnace. Slow firing cycle.
(3) Dirty substrate. (3) Clean. There is no substitute for a clean substrate.
(4) Mixing incompatible materials. (4) Be sure you know what you are mixing. When in question, ask!
(5) Contamination, either organic or inorganic, usually covered, causing localized blisters but in sufficient quantity, can be dispersed throughout the coating. (5) Same as A (3). Keep containers covered.
(6) Coating too heavy. (6) Add thinner or extender.
Blocking A. Coating material not dry. A. Improve drying process.
  B. Substrate stacked prior to firing while still too warm. B. Add more cooling before stacking.
Bloom A. On glass surface, a result of moisture and/or atmospheric attack. A. Keep glass dry; fabricate as soon as possible. There is no method currently in use for removing the stain.
  B. On silver stains: overfired. B. Reduce firing temperature and/or increase speed through firing cycle.
Blur   See Smear.    
Breakage A. Improper heat treating. A. Adjust heat-cooling cycle.
  B. Damaged glass surfaces or edges. B. Improve handling procedures.
  C. Improper match of coefficient of expansion of the coating to the substrate. C. Consult supplier.
Chain marks A. Excessive heat during firing cycle. A. Lower the temperature.
  B. Firing cycle too slow. B. Speed up the cycle.
  C. Coating material too high maturing for substrate and cycle. C. Consult supplier.
Checking   See Cracking.    
Clogging   See Pinholes D. and N..    
Coating too heavy A. Coating too viscous. A. Add thinner and/or extender.
  B. Screen mesh too coarse. B. Use finer mesh screen, monofilament fabric.
  C. More pigment (and cost) than necessary. C. Consult supplier.
  D. Dull squeegee. D. Sharpen squeegee.
  E. Insufficient squeegee pressure. E. Adjust downward pressure.
Coating too thin A. Excessive thinning of coating material. A. Reduce amount of thinner used. Change to more effective thinner.
  B. Screen mesh too fine. B. Use coarser mesh monofilament or stainless steel fabric and dull squeegee.
  C. Insufficient pigment mix C. Unlikely, but perhaps can be increased if all else fails. Consult supplier.
Color variation A. Too much heat for coating being used. A. Reduce heat or speed up firing process. Consult supplier for coating with proper firing range.
  B. Unstable pigments. B. Consult supplier.
  C. Contamination of substrate. C. Clean substrate.
  D. Contamination of coating. D. Keep containers sealed.
  E. Minute blistering. E. See Blister.
  F. Underfired F. Increase heat, slow down firing process. Consult supplier for coating with proper firing range.
Cracking A. Coating film too heavy. A. Apply thinner coating.
  B. Shrinkage of coating film due to fine particle size of solids. B. Apply thinner coating. Consult supplier.
  C. Moisture in coating material. C. Consult supplier. Keep containers sealed.
  D. Condensation on substrate. D. Store substrate in screening and/or firing area 24 hours prior to processing.
Craters A. Water droplets from air lines; sprinklers; ; leaking pipes; condensation from ventilators, air conditioners, water lines, coolers, beverages. A. Clean air lines, use filters, wrap pipes, keep sources of water away from immediate work area.
Also:
Dimples
  B. Oil droplets from air lines, lubricants, thinners, hand cleaners. B. Clean air lines, use filters. Avoid excess lubricants on equipment. Thin the coating materials away from usage areas. Use hand cleaners away from machines, conveyors, racks, screens, open containers of coating materials.
  C. Solvent droplets from thinners, extenders, hand cleaning, wash-up. C. Remove decorated parts from areas where solvent is being used.
Crawling A. Poor wetting of the substrate. A. Add wetting agents. Consult supplier.
Also:
Creeping,
Fish eyes,
Pull-back
  B. Contaminated supbstrate. B. Clean substrate.
  C. Presence of silicone lubricant. C. Clean substrate. May require heating the substrate to 800°F if cleaning alone does not remove contamination.
Crazing A. Improper match of coefficient of expansion of the coating to the substrate. A. Consult supplier.
Creeping   See Crawling.    
Crizzle A. Moisture in the undercoat. A. Avoid temperature extremes before firing. Contact supplier if condition persists.
Dark reaction A. Coated material has exceeded shelf life. A. Replace with new material.
(U.V. Ink)
  B. Coating material was stored at elevated temperature. B. Change storage area to cooler (-room temp.) location.
  C. Formulation unstable. C. Consult supplier.
Delamination A. Contaminated substrate. A. Clean or replace substrate.
Also:
Ragged lines,
Sawtooth
  B. Overcured base coat. B. Reduce cure time.
  C. Gross mismatch in expansion between layers. C. Consult supplier.
Digs A. Impact with a foreign object. A. Change storage location to a safer, protected area. Instruction on safe handling. Use a cover plate during storage.
Dimples   See Craters.    
Distorted image A. Too much squeegee pressure. A. Reduce squeegee pressure.
  B. Insufficient screen tension. B. Replace screen.
  C. Weak screen frame structure. C. Obtain more rigid frames.
  D. Distorted artwork. D. Obtain new corrected artwork.
  E. Too much off-contact. E. Reduce off-contact. Replace screen.
Drying in A. Coating dries too fast. A. Use slower drying coating. Consult supplier. Use flood coat immediately after printing.
  B. Operation is too slow. B. Speed up the process.
  C. Too much air flow over the screen. C. Redirect air flow from fans or other sources.
Dull finish A. Underfired. A. Elevate temperature. Reduce speed through furnace. Use lower maturing colors.
  B. Blistered. B. See Blister.
  C. Surface contaminated by inorganic dust. C. Keep clean (dust covers).
  D. Devitrification - crystallization. D. Reduce heat, increase speed through furnace, use higher maturing colors.
Film thickness variation A. Improperly tensioned screen fabric. A. Tighten or replace screen.
Fish eyes A. Waterspots on substrate when using oil base coating. A. Clean substrate.
Also:
Crawling.
  B. Oil spots on substrate when using water base coating. B. Clean substrate.
  C. Silicone lubricants and additives. C. Avoid the use of silicone containing lubricants where possible. Do not over lubricate. Be very careful and accurate when using silicone containing additives.
  D. Foreign materials on substrate. D. Clean substrate.
  E. Improper mix of coating materials. E. Improve mixing procedures.
Flaking A. Coating film too thick. A. Reduce film thickness with finer screen, thinner screen emulsion, thinner coating viscosity, or harder squeegee.
  B. Damage to coating film from impact, handling or stacking. B. Handle with care.
Ghost   See Smearing.    
Halo   Silver paste is overfired or contamination on glass surface. See Smearing.   Reduce firing temperature.
Heavy edges or incomplete print A. Screen frame too small for image size. A. Use larger frame or smaller images.
  B. Too much off-contact. B. Reduce off-contact gap.
  C. Squeegee too short. C. Use longer squeegee. Squeegee should extend 1 inch beyond image on both sides.
  D. Variation in thickness of substrate. D. Use softer squeegee.
  E. Improper alignment of printing head and table. E. Align printing head and table.
  F. Clogged screen. F. Clean or replace screen.
  G. Insufficient squeegee travel. G. Lengthen distance of squeegee travel beyond image area.
  H. Uneven squeegee blade. H. Sharpen squeegee.
  I. Improperly tensioned screen fabric. I. Obtain properly tensioned screen or retension.
Hickey A. Airborne contamination, dirty substrate, foreign particles in coating, poor housekeeping. A. Enclose screen room. Clean substrate immediately before using. Do not put used coating material back into container with fresh coating. Clean screen area regularly. Keep non-essential personnel out of screening area.
Lifting A. First layer not adequately cured. A. Increase cure time/temp.
  B. Solvent in second layer is too aggressive. B. Consult supplier.
  C. Contaminated substrate. C. Clean substrate.
Mesh marks A. Insufficient levelling or flow of coating material. A. Increase time between printing and drying.
  B. Improper thinner. B. Consult supplier.
  C. Viscosity too high. C. Thin the coating material.
Moire A. Uneven drying of coating. A. Add drying retarders.
Also: Shorelining
  B. Thin print. B. Use thicker coating material or coarser screens.
  C. When printing two or more coats, the mesh patterns in the screens tend to line up almost (but not quite) perfectly. C. Consult screen supplier to mount screen mesh on frames with mesh running at one angle to an edge for first coat, and at other angles for additional coats. Angles to be used should be determined by screen supplier and are based on mesh count, screen tension, etc.
  D. When printing narrow lines and/or fine detail, the line width of the detail and mesh count of screen are not compatible. D. Change screen mesh. Consult supplier.
Orange peel A. Coating material too visous. A. Thin the coating material.
  B. Coating material too tacky. B. Thin the coating material or add extender.
  C. Coating material lacks proper flow. C. Add flow control agents. Consult supplier.
Overcure A. Too much heat. A. Reduce temperature.
  B. Too much exposure. B. Shorten cure time.
Peeling   See Cracking, Alligatoring..    
Pinholes A. Bubbles which appear during the application process and break during the drying process, leaving a hole. A. Reduce visosity of coating by thinning or adding flow control agents which reduce surface tension.
  B. Organic particles which burn out during firing leaving a hole in their place, such as partially dissolved vehicle components. B. B, F, I, L are processing variables which can be controlled by the supplier to a limited degree. H, and J also lie with the supplier. Due to high temperature processing, refractories are a must for containment. Also, the high temperatures required for the chemical reaction of pigments sometimes produces small metallic particles in the batch which cannot always be separated out.
  C. Too much heat, too fast. Causes fusion before the organic vehicle has completely burned away. Causes a rupturing of the surface skin from the combustion gases. C. Use preheat if at all possible. Use higher melting ceramic. Slower speed at lower temperature.
  D. Particles of dust and other foreign matter on the substrate or in the coating. Airborn dirt of all types. D. D, H, J - Operate in clean room during application and drying. Once dry, surface dust will not cause pinholing. Improve general housekeeping methods.
  E. Minute cracks in the coating. E. See Crizzle.
  F. Soluble chemical compounds in the make-up of inorganic pigments which decompose in heat. F. See B above.
  G. Small fish eyes. G. See Fish eyes.
  H. Metal particles. H. See B and D above.
  I. Agglomerated particles of pigment. I. See B above.
  J. Particles of refractory. J. See B and D above.
  K. Glass chips. K. Same as D above.
  L. Poor dispersion of pigments in mix. L. See B above.
  M. Printing screen plugged, preventing passage of coating materials. M. Clean or replace screen.
  N. Poor mixing of coating materials. N. Improve mixing procedures.
  O. Static electricity. O. Ground coating equipment and substrate.
Pullback, ragged lines or lettering   See Crawling.    
Also:
Distorted image, Sawtooth
  A. Insufficient thickness of emulsion on screen. A. Request screen supplier to apply heavier coat of emulsion.
  B. Plugged or clogged screen mesh. B. Clean or replace screen.
  C. Coating material drying out in screen mesh. C. Clean or replace screen. Use slower drying coatings if available. Add retarder.
  D. Failure of screen supplier to completely wash out image duringmanufacture of screen. D. Return screen to supplier. Wash out obstruction with water or Clorox bleach.
  E. Over-exposure of emulsion during manufacture of screen. E. Return screen to supplier.
  F. Poor artwork. F. Obtain new corrected artwork.
Railroading A. Squeegee jumps from line to line on screen, causing screen to jerk and distort or smear the image. A. Angle the squeegee so it doesn't hit the line straight on. Angle the image in the screen. Softer squeegee will reduce the severity of the problem. Use higher tensioned screens.
Rough image   See Ragged lines or lettering.    
Rubs A. Handling damage. A. Provide instruction in handling the coated product.
  B. Abrasion from conveyor. B. Make sure the equipment is free of any obstruction and all sections of the conveyor are running at the same speed. Provide separation material for substrate when stacked.
Running   See Sagging.    
Sagging A. Poor centilation of combustion gases during burnout portion of firing cycle. A. Improve ventilation in early stages of firing operation.
Also:
(Slumping)
Running, Weeping, Creeping
  B. Improper or sub-standard idgredient(s) in vehicle formulation. B. Consult supplier.
Sandy finish A. Underfired. A. Increase temperature, reduce speed or consult supplier for lower maturing coating.
  B. Insufficient film thickness. B. Use thicker coating material or coarser screen.
  C. Inadequate blending of dry ingredients. C. Consult supplier.
  D. Blistered. D. See Blister.
  E. Dry print. E. Thin coating material, flood screen, increase printing rate.
Sawtooth   See Ragged lines or lettering.    
Scallop   See Crawling.    
Shadow   See Smearing.    
Shorelining   See Moiré.    
Sliding A. Moisture - condensation. A. See Blister, subsection causes A(1) and A(2) and solutions for same.
Slipping   See Sliding.    
Slump   See Sagging.    
Smearing A. Dull squeegee. A. Sharpen squeegee.
Also:
Ghosting, Shadowing, Halo, Blur
  B. Insufficient screen tension. B. Replace screen.
  C. Screen not locked into place. C. Tighten clamps or bolts.
  D. Too much squeegee pressure. D. Reduce pressure.
  E. Squeegee to soft. E. Install higher durometer squeegee.
  F. Too much screen peel-away. F. Reduce peel.
  G. Coating material too thin. G. Add less thinner. If too thin when received, ask supplier to furnish more viscous future lots.
  H. Movement of substrate under screen. H. Make sure stops are secure and substrate is tight against stops. Check level and flatness of printing table. Make sure squeegee travel on print stroke is toward stops, not away.
  I. Delayed screen snap-off. I. Check screen tension. Make sure squeegee travels beyond end of image. Check and adjust peel-away. Coating material may have to be thinned to reduce tackiness.
  J. Squeegee blade distorted. J. Use higher durometer squeegee. Reduce amount of blade exposure from holder. Stiffen squeegee blade with metal strips.
  K. Too much off-contact between screen and substrate. K. Reduce and/or make parallel off-contact gap.
  L. Printing table not secure. L. Lock down printing table.
Spotting A. Water droplets from washer. A. Adjust/repair washer. Wipe substrate before coating.
Also:
Watermark
  B. Contaminated substrate. B. Clean substrate.
  C. Stained glass (from exposure to moisture). C. If stain is light, may wash off; if heavy, discard glass.
Starlight A. Coating material too viscous. A. Add thinner.
Also: Starburst, Mesh Marks.
 
  B. Insufficient squeegee pressure. B. Increase pressure.
  C. Insufficient flood. C. Increase flood pressure (or change angle of flood bar).
  D. Inadequate flow of coating material. D. Add flow agent.
  E. Bubbles caused by peeling action of screen as mesh pulls free of coating. E. Add flow agent; increase off-contact distance between screen and substrate.
  F. Excessive heat in earliest part of the firing cycle. F. Reduce heat (or line speed) in forst zone(s) of furnace; increase aspiration.
Stringing   See Cobwebbing.    
Sulphide staining A. Staining by sulpher containing atmospheric contaminants. A. Use more chemically resistant coatings.
  B. Sulpher containing packaging materials. B. Change packaging material. Use more chemically resistant coatings.
        Note: It is sometimes possible to salvage products with a very light sulphide stain by refiring, whereas a heavy stain usually damages the coating surface upon refiring.
Tearing   See Cracking, Alligatoring.    
Watermark A. An accumulation of soluble salts on a glass furnace. A. Inspect and repair washer. Remove any signs of water before storing or decorating glass.
Also:
Spotting
Weeping   See Sagging.    
Whiskering   See Cobwebbing.