Two variations of contrastive glass painting are around today - water-based and non-water based. Both have a good range of colors and are mixable within their classes.

When applying an outline, you can choose one of three different ways while glass-painting your birthday cards:

Outline Stickers - Novices to glass painting should find these perfect and are best applied on flat, level surfaces. Beginning in one corner, slowly peel up the sticker, being careful not to stretch or distort it and apply it to the clean glass surface area of your birthday cards.

Glass paint outliner - These are applied by squeezing the outliner out of a tube to give a thin outline. They are available in a choice of colours. They are able to be applied as an outline for your design prior to paint being applied or piped over a pre-painted surface as fine detailing.

Leading Tape - Doors and windows usually necessitate this type of outliner.

Technique:

Prior to starting to paint, remove any specs of dust and grease from the glass area of the birthday cards, thereby ensuring good adherence. A solvent such as white spirit or methylated spirit must also be used.

When working on a flat surface such as a birthday card, designs are usually traced straight through. It is easier to work on a flat surface, so try to lay the birthday card of a horizontal surface. 

To create a straight line with a glass paint outliner touch the nozzle onto a glass surface followed by applying a soft even pressure, lift the nozzle away from the surface and stretch out the outliner along in a straight line. Tap the nozzle down on the glass surface when you are ending the line. 

When completing sections in between outlines on the glass section of your birthday cards with a paint brush, apply paint generously by peddling the paint or adopting a pipette. This is able to offer a flat, stained-glass effect. To obtain a lighter color paint, weaken with water for the water based paints or gloss varnish for the non-water based paints.

Always pour paint into a palette rather than straight from the jar. In order to prevent colours becoming dirty or diluted. Glass paint can also be applied using a sponge, but birthday cards tend to have smaller areas, whereby this method is usually best for wider areas.

To finish, a coat of varnish can be a used to protect solvent based paints, which is obtainable in either a matt or gloss finish. Gloss finish is usually most popular for birthday cards, however some individuals might be hoping for something exclusive. Gloss varnish is sometimes also used as a colourless thinner, which will obtain pastel shades, while keeping the colour depth and any transparent effects. The matt varnish provides a finish similar to frosted glass. Adding beads or sequins may be a nice final touch and should be added while the paint is wet. The damp paint is a good substitute for glue. You can also add glitter by sprinkling it over the wet paint giving your birthday cards that extra bit of glisten.

Memo: Whilst adopting these methods in conditions other than for your birthday cards, glass paint ought to be applied simply for ornamental items, the colours aren't dishwasher resistant. It can, nonetheless be shined by wiping with a moist flannel.