Rub Removable Silver prints A brief explanation as to why prints under certain conditions appear to show the image beneath the opaque silver ink Geoff Page July 2001

Clay Coated Paper/board Offset litho print CROSS SECTIONAL VIEW Avoid absorbent papers for Rub Removable prints. Check absorbency by licking the paper 1) Litho prints

2) Rub Removable silver printed over the Litho print to obscure the design CROSS SECTIONAL VIEW The litho inks must be fully dry before the Silver can be applied. Oxidation drying inks may take some days, leave at least 24 hours

As the solvent evaporates, some will soak in to the board. Some solvent will soak through the litho print but not as fast as the unprinted areas, so different drying rates are then established CROSS SECTIONAL VIEW

The silver pigment is made of aluminium platelets that are “leafing” to give maximum opacity. The tendency is for the platelets normally to lie flat but due to this difference in drying rates, the platelets can lie at a slightly different angles from the printed to unprinted areas CROSS SECTIONAL VIEW

Light hitting the print film is then reflected at different angles. This can give the visual effect or illusion of being able to see the design that is under the silver. CROSS SECTIONAL VIEW

Although the print is a uniform colour, the different light reflection allows an image to be seen. View from directly above the print, face on RR SilverRR Silver over Litho print

One solution is to overprint the silver with a “disruptor” pattern of dots or wavy lines to mask the effect Fast oxidation offset inks, or Colorstar CS inks can be used

Another solution is to print a layer of varnish enough to seal the surface of the board and cover the litho print Varnish layer CROSS SECTIONAL VIEW

The varnish layer helps stop the solvent absorption In to the board during the drying phase. UV litho, UV screen and certain solvent based varnishes can be used. Avoid water based aqua seal type varnishes CROSS SECTIONAL VIEW

Another alternative is to print another litho colour so there is not such a contrast and help seal the board.This will help the “silver platelets” align more evenly, so reducing any leafing effect Extra Litho colour

CROSS SECTIONAL VIEW For maximum prevention; Extra Litho colour Sufficient layer of varnish Disruptor pattern overprint Disruptor pattern on reverse side

Another cause of image appearance on the silver can be when “spot printing” This will give pressure points in the stack. The extra film weight areas of the litho text, overvarnish and silver, give the “spots” higher relief than the rest of the print. Because of this, the weight of the stack can then cause marking on the soft silver surface at the interface with the back of the board. An image can form when the text under the silver is a slightly higher film weight and so this area absorbs even more pressure causing the silver to develop a mark of the image underneath Remedy? Small stacks, stack at different angles to avoid pressure points, ensure prints are fully dry, avoid stacking “hot” prints, do not "band wrap" before prints are guillotined Pressure points in the stack

Board Litho Varnish Silver Spot images causing pressure points in the stack. This may mark the silver at the interface with the board STACK PRESSURE Leaves dull mark

In Conclusion: Paper: Avoid absorbent papers and cards Seal with suitable varnish, film weight must be sufficient Prints: The litho inks must be fully dry if oxidation drying type. Leave for a minimum 24 hours before overprinting. Ensure opacity of the silver is high enough. Print a “disruptor” pattern over the silver to mask any effect Avoid pressure points if “spot printing”