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I have made this jar using plaster:

enter image description here

I painted it with plastic white paint as a base, and then applied this gold metallic paint.

Now I want to paint some horizontal brown lines using oil-based brown paint and a small brush, but I need some ideas and help on how I can get (a) perfect horizontal line(s).

I think it will be hard to do so using painting tape (by taping 2 parallel horizontal lines using painting tape and keeping around 10 cm between them, then painting the area between the 2 pieces of tape), as it will be hard to maintain equal space between the 2 parallel tapes. I will then also run the risk of removing or damaging the gold paint after removing the tape.

Is there another method to do so?
Or are there any online stencils that I can order which can help me in doing what I want?

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3 Answers 3

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Build a structure from common materials, i.e., books, blocks of wood, etc., at the height necessary to match your objective line. You can use a pencil secured to the structure, making contact with the pot, rotating manually the pot, scribing each line as required.

At that point, you can trust your steady hand, or use the line to apply masking tape.

You may be able to use vehicle pinstripe tape, as it is stretchy for the purpose of following vehicle body panel curves and distortions. Vehicle pinstripe tape would be applied along the pencil lines, providing the masking you desire, to restrict your paint lines.

It's a modification of Triplefault's method (from Home Improvement SE) with fewer materials and purchase expenses.

Duplicated in Home Improvement SE, but probably better suited here.

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    A steady hand might be better than tape because it curves in both axes. The nature of the curve means tape is possible but I'd rather not work with wrinkled tape
    – Chris H
    Feb 25 at 10:24
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    I agree, and as the OP noted, risk of damage from the adhesive.
    – fred_dot_u
    Feb 25 at 14:37
  • @fred_dot_u thanks for the reply .. but are not there any stencil which can stick to the surface and allow me to paint the line ?
    – John John
    Feb 25 at 15:11
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    As other commenters have noted, the curvature will cause some problems with wrinkling and distortions. See edit to my answer.
    – fred_dot_u
    Feb 25 at 17:16
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A globe-shaped object is hard to create a stencil for because it curves in two directions. To have access to the painting surface, the stencil shape would be a cylinder.

If you make the stencil from tape, it can be difficult to position it because only the very edge of the tape can form a cylinder; if any other part of the tape grabs the surface while you're positioning it, the tape won't form a clean, uniform circle around the object. Once the edge is pefectly in place, the rest of the tape can by crumpled against the object. Tape also runs the risk of pulling paint off the surface if the paint isn't well adhered or the surface is weak.

Vehicle pinstriping tape is suggested in fred_dot_u's answer. That is stretchy so it can conform to a 3D surface. But the adhesive is designed for automotive paint, which is very tough stuff, adhered to a tough surface. You would want to experiment with it, or any tape, on painted plaster.

My suggestion is to use a rigid cylinder that isn't adhered to the object where that will work, or tacky putty. The tacky putty I'm referring to is a putty that sticks non-aggressively to a surface and is designed to not stain or damage the surface. There are various such products sold to stick light-weight objects, like photos, temporarily to painted walls, or to seal weatherproofing film to painted walls. Some of these putties can leave a stain if left in place for a long time, so you would want to test the product in an inconspicuous place (I haven't recently used any, so can't make a specific recommendation).

You can use the tacky putty in combination with a rigid cylinder to create a mask (position the cylinder, then press a band of putty against the cylinder edge to create the stencil edge, then remove the cylinder), but you could also use it with the kind of setup described in fred_dot_u's answer, where you would press a band of putty around the object, then use a knife in that setup to precisely cut it for the edge of the stencil, and peel off the putty in the painting area.

With a rigid cylinder or tape, use thick paint so it doesn't wick.

Cylinder approach details

Measure the diameter at the top and bottom of the area where you want a paint band. Make a cylinder of each diameter from sheet material with enough strength to support the weight of the piece, like cardstock. Ensure that you start with material that has a straight, clean edge.

If the paint band is around the equator, support the piece on the bottom cylinder, and position the top cylinder so the two cylinders create a stencil for the paint band. Note that the top and bottom cylinders don't need to be the same size, so the paint band doesn't need to be the same distance up and down from the equator.

enter image description here

If the band will be entirely north or south of the "equator", position the larger cylinder, and use its edge as a guide for applying the putty (or painter's tape). Remove the cylinder and then support the piece on the smaller cylinder so it acts as a stencil. The image below shows the putty/tape and cylinder at the top, but you can flip it upside-down so the cylinder acts like a stand.

enter image description here

Note in the diagram that when you need to use tape, the edge you want perfect is on a smaller diameter than the other edge of the tape, so it's almost impossible to lay down tape perfectly. Using putty solves this problem.

As Elmy notes in a comment, you need a method to ensure that the cylinders and object are accurated aligned horizontally, like using a level. You also need to be careful to keep the positioning secure so nothing shifts while you're painting.

Last resort masking

If you are concerned that any form of tape or putty might damage the gold, and don't want to risk trying to touch it up, here's a last resort method to safely mask. Wrap the piece tightly in plastic wrap. Then apply painters tape tightly in the area and vicinity of where the band will be, overlapping where the edge will be.

Measure the diameter after it's wrapped to make the cylinder. Use the cylinder to identify where the edge of the band will be, and cut the wrapping with a knife (if that creates a groove in the plaster, it will be filled with paint). Remove the wrapping from the side you will paint, and use the smaller cylinder to complete the stencil. The painters tape will peel off the plastic film to remove the mask.

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    They should probably use a spirit level to make sure 1) the suspension construction itself is level, 2) they suspended the jar perfectly level and 3) the jar or construction doesn't move during the painting. It's very easy to think you suspended the jar horizontally only to be shocked at how crooked your line turned out.
    – Elmy
    Feb 25 at 5:21
  • @fixer1234 but aren't there any stencils which can stick to the surface and allow me to paint the line, and to then remove the stencil? It seems it will be the easier thing to do?
    – John John
    Feb 25 at 15:11
  • @fixer1234 can you draw a quick sketch about your method so I can understand it better?
    – John John
    Feb 25 at 15:13
  • @JohnJohn, a globe-shaped object curves in two directions. A cylinder shape is one side of a stencil. You can make it out of something rigid, or make it out of tape and then press everything that isn't the edge against the object. I added some images for clarification. Another material for the stencil would be a slightly tacky clay or putty that doesn't bleed any material that could affect the surface color or finish. Press a band of it around the object, then use a turntable as described in fred_dot_u's answer to cut a precise edge with a knife and peel away what's in the painting area.
    – fixer1234
    Feb 25 at 21:54
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Put the project in the middle of a lazy susan.

Build a structure on the table to hold the brush at the right height this could be your hands and arms, but I'm envisioning books or blocks of wood to improve the repeatability

Put the brush against the project

Spin the lazy susan.

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    this might work on paper,, but will the line have a straight boundaries? i mean when i move the lazy susan,, some brush hair might move up or down causing the line to look not straight ..
    – John John
    Feb 25 at 16:11
  • This might be a try and see, I'd expect the pressure, size and type of brush to be important parameters. You are emulating using a lathe
    – Anthony
    Feb 25 at 18:29
  • I'd be more worried about wobbles in the bearings, because there's no need for a lazy susan to stay perfectly flat and the bearing race is moulded plastic. A record player turntable might be better
    – Chris H
    Mar 7 at 10:47

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