Spray Chrome Troubleshooting Guide
At AngelGilding we think that the more you understand a process - and the science behind it - the more likely you are to succeed.
We have listed the most common problems with creating a front surface silver mirror and the causes and solutions to those problems. We have detailed explanations at the bottom of the page.
To answer one very frequently asked question -- yes, you can certainly use our chemicals in another company's spray on chrome machine. Just rinse the machine thoroughly with distilled water first and be sure to follow our mixing instructions!
Spray Chrome Troubleshooting Guide
|Dull gray all over||Dull or matte surface||The surface must be high gloss - like glass - before you silver it. Silver does not make a dull surface reflective.|
|'Orange peel' or nibs in the base coat||Base coat not applied correctly||Air pressure from the gun is too high. The gun is too close. Uni-Coat has started to dry in the gun.|
|Gray and speckled||The surface did not "wet" evenly so the Sensitizer (Tin) did not deposit evenly.||Start with a clean surface. Apply Wetting Agent and then apply a generous layer of Sensitizer on top of the Wetting Agent.|
|Small gray splotches in the silver||Silvering bare plastic||Some plastics and some base coats may not work well with silver.|
|Yellow or brown stains||Too much Sensitizer (Tin) left on the surface||Rinse the Tin and then rinse it again. You will not be able to rinse off the sensitizing layer that attaches the silver to the surface.|
|Blue areas||The chemicals are not in balance||Check that your spray guns or pump bottles are delivering equal amounts of Silver and Reducer. Be sure you have mixed the chemicals properly.|
|Dark gray in some areas||Silver was not applied evenly||Spray more silver in the dark areas to even out the tone. You can always add a little more silver.|
|Matte white areas||Too much silver||Stop silvering as soon as you have a bright, even coat. Adding more silver usually makes the problem worse.|
|Dull and dusty||Silver applied at close range
Not enough rinsing
|Hold the wands or spray guns at least 1 foot (30 cm) from the surface. Spray in light, even layers. Rinse well between layers.|
|Silver rubs off very easily||Problems with the Sensitizer (Tin)||A good silver layer is difficult, but not impossible, to rub off. Use fresh Tin. Rinse the Tin very thoroughly.|
|Pale gold color after top coating||You used an un-tinted top coat.||This is an optical quality of silver metal (see below). Tint your top coat with a transparent blue or violet dye.|
|Surface wrinkled after top coating||The base coat did not cure||Allow the base coat to cure fully before silvering. You used an incompatible base coat.|
Uni-Coat flows out to flawlessly smooth, glassy surface when it is applied correctly. The air pressure coming from your HVLP gun should not be greater than 10 psi. Hold the gun 8 to 10 inches away and at right angles to the surface. Apply the Uni-Coat in a sweeping motion. Apply one double wet layer - a thin layer adheres better than a heavy layer. Make sure the entire surface is wet - avoid dry misting which will show up as a matte surface under the silver. Applying a heavy layer can also result in runs and drips.
Make sure the Uni-Coat has not begun to dry in the gun. Partially dried Uni-Coat shows up as small nibs on the surface. The temperature of your work space greatly affects the drying time of the Uni-Coat. Clean the gun immediately after use by spraying clean acetone through it.
The silver deposited on the surface is thin - 50 to 100 nanometers or 600 times thinner than a human hair. It is much too thin to fill in any surface imperfections on your piece. If you want the silver to look like a mirror, the surface that you silver must look like glass.
Secondly, the silver will make any imperfection - any bump or dent in the surface - much more obvious because the light that hits the bump will be reflected back on a different path - which is to say that the 'angle of incidence = the angle of refraction.' Uni-Coat applied to a carefully prepared surface give you the glassy texture you need to create a perfect reflection.
Water has a high degree of surface tension; the water molecules would rather stick to themselves than to the surface. Most plastics also have a high degree of surface tension so they repel water - they are hydrophobic. When you cover plastic with water, the water beads up and runs off.
A wetting agent - also known as a surfactant - is a substance that breaks the surface tension in water. There are many kinds of surfactants designed specifically for different surfaces. Our Wetting Agent is very generic so it works on most surfaces. However, it only works when it is mixed with the water-borne chemical you are trying to apply - in this case the Sensitizer or Tin for Silver. So you must allow the two substances to mix on the surface by applying the Wetting Agent and then adding the Sensitizer.
We have tried pre-mixing the two chemicals, but the chemicals perform better when they are each at their own dilution ratios. Our two-step process is a reliable way to ensure that they both are both able to fully do their work.
If the plastic surface you want to silver is already high gloss, you may not need to apply a base coat. You may be able to apply the silver directly to the bare plastic. We have done this successfully on many plastics.
However, we have found that on some pieces, no matter how well we clean the surface or how much Wetting Agent we apply, the silver still has small gray speckles in it. We have not yet found the exact cause for this. We have found that we can fix the problem by using Uni-Coat base coat.
if you have the same problem, you do not need to discard the piece. Just clean off the bad silver with Silver Remover clean and dry the piece carefully, and apply Uni-coat base coat.
Steam distilled or de-ionized water is often available at your local grocery store. Not all bottled water is suitable for mirroring. The bottle you buy must be labeled as "distilled" "de-ionized" or "reverse osmosis". You can pay for a TDS (total dissolved solids) meter if you like, but we have a simple test for water purity and a further discussion on how water is purified on our Water Purity page.
The sensitizer layer is invisible but it is essential to the silvering process. There are several important facts about it.
- The Tin (Sensitizer) layer chemically attaches the silver to the substrate. If the surface is not completely covered with Tin, the silver will rub off very easily. The surface must be clean so the Tin can attach and the water that carries the Tin must be able to contact the surface - see Wetting the Surface.
- The Sensitizer must be diluted according to our instructions. If it is too strong, the silver will not deposit evenly. Chemistry is like cooking - your hamburger tastes better with the right amount of salt .
- If there is any Sensitizer solution left on the surface when you add the silver, it will react with it and cause the silver to deposit unevenly leaving brown and yellow stains. Rinse, and then rinse again before you add the silver - you can not rinse it too much.
- Sensitizer combines easily with the oxygen in the water and the air. When it does, it converts into an insoluble form that will not attach to the surface. Fortunately for us, this form of the chemical is yellow rather than white so it is easy to see when the Sensitizer is no longer good for silvering.
Our silvering chemicals are robust. Having the guns out of balance by a small amount will not affect the silver coat. Before you worry about the balance of the guns, make sure that your problems are not caused by some other problem.
Adjusting our Pump Spray Assembly:
- The bottles must contain about 2 fluid ounces - they do not work well when they are almost empty.
- Both bottles must be fully pressurized. Forcing the piston can break the seals on the pumps.
- The mist adjustment knobs on the tips of the wands should be finger tight to deliver a fine mist rather than a jet.
- We include a pump bottle repair kit with our Pump Spray Silver Kit and our Basic Spray Chrome Kit.
Adjusting our Center Handle Silvering Gun:
- Use distilled or de-ionized water for this test. Do not use silvering chemicals or tap water.
- Measure 500 mL of distilled water into each bottle and attach the bottles to the gun
- Point the gun into a sink or tub, squeeze the trigger and hold for about 30 seconds.
- Remove the bottles from the guns and set them flat on your bench.
- If the bottles have not lost equal amounts of water, adjust the knobs on the end of each gun and try the test again.
Silver adheres to silver. If you want a heavier layer of silver, you can always spray on a second layer even if the first layer is dry. You will get a more even deposition if the first layer is fresh and still wet, but the chemistry will work on a dry surface. You do not need to re-tin the piece.
When you are working on a front surface mirror (spray chrome) go very lightly with this step adding silver only in the areas that need it. Too much silver can produce a white, cloudy appearance.
When you are working on a second surface mirror (looking through the glass or plastic to see the silver) the only danger with applying more layers is that the silver will become so heavy it peels off when you rinse it. This does not happen often, but it is possible.
As we mentioned above, silver adheres to silver. The silver crystals build up exponentially fast. As the 'mountains' of silver crystals grow, the surface becomes rough and less reflective. Instead of a perfect mirror, you begin to see dull, white areas. Adding more silver makes the problem worse. Because the silver is so thin (see above) burnishing does not solve the problem.
The best way to fix the problem is to avoid it by applying the silver in thin layers and rinsing it between each layer.
This problem is similar to the problem of white "clouds" above. The silvering reaction takes place on the surface when the silver and reducer mix together. The process is fast, but not instant. You will have better results and waste less silver if you give the chemicals time to mix and develop evenly. Hold the wands or spray gun far enough away from the surface so that the chemicals can mix in the air and fall evenly. Using less force and taking your time will give a more uniform coating.
Unlike aluminum, steel or chrome, silver metal has an optical property called "thin film interference". When it is covered with any thin clear film - including distilled water - it absorbs blue light and reflects yellow light. You can see this in action by looking at wet silver next to dry silver. The "wet silver / dry silver" test proves that the yellowing is not caused by any substance in the base coat or top coat.
Because silver formed by the mirroring process is pure elemental silver, it is not chemically possible to add a tint to the metal. The only way to counteract the effect of thin film interference is to add a tint to the top coat. Since the light coming from the silver is yellow, the logical color to add to the top coat is blue because it is the opposite of yellow in terms of light. However, most color-fast blue dyes have a tendency to look slightly green in a dilute concentration. The reddish tones in a violet tint will counteract the green tones in the blue, so we recommend adding violet dye to the top coat.
Make all color judgements by viewing the piece in full daylight without artificial light. Incandescent and fluorescent lights tend to make any surface look yellow.
Wikkipedia has a full explanation of Thin Film Interference
See our Clear Uni-coat Product Data Sheet for information on air- drying or force-drying the base coat. The base coat cannot dry or cure after you apply the silver. We recommend at least 12 hours of drying time at 70 ° F (20 ° C) before silvering.
If you use Uni-Coat top coat (clear or tinted) over another base coat, the two might be chemically incompatible even if the other base coat is perfectly cured. The same is true with applying Uni-Coat over an unknown bare plastic. As always, you can save yourself a lot of trouble later by taking the time to test all the variables first.
If you have any questions or proposed corrections to this Guide, please contact us.
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