Filling knives can be used as levers where their thin blade fits small gaps, but only low force is needed. Use of multiple scrapers increases total levering force. Wide blades and low force minimises risk of damage to the workpiece. Useful for removing decorative timber trim.
Scraper behaviour is all about relative hardness. When 2 materials scrape against each other, the softer one deforms, with little effect on the harder one. This means 2 things:
- to be an effective cleaner the scraper must be harder than the dirt/paint etc
- to avoid risk of damage the scraper should be softer than the workpiece
Hardness is measured in mohs, a non-linear scale with with diamond at 10 mohs, and soft talc at 1 moh.
With many surfaces, microscopic damage matters. It causes:
- loss of gloss or shine
- for see-through materials, complete loss of clarity
- it makes cleaning rather harder, which is an issue in the kitchen, and with plastic surfaces
- gradual wearing off of thin surface coatings
For some surfaces, microscopic damage doesn't matter. This is true of wood, and thus metal scrapers are usually used. The tough hard steel is long lived and rarely needs its edge grinding. Wood is low on the mohs scale at under 2.5.
Glass and see through plastic are especially vulnerable to scraper action, since the results of surface damage are so visible. Glass is a hard material at 5.5 mohs, but steel scrapers can sometimes cause scratching and abrasion as they're just as hard. Where glass is puttied it doesn't matter, as its covered over, and tiny scratch marks are a very small matter. Where the effects are more noticeable, steel scrapers are better avoided. Copper and aluminium edges can remove paint and dirt, albeit with a fair bit of wear to the scraper edge.
Plastics vary significantly in hardness, and are softer than metals. Sometimes a thin softer plastic finish on a hard surface makes its softness non-obvious - non-stick cookware is an example. Plastics also frequently need to retain their shine to look good. For these reasons only the softest of scraper material should be used occasionally on plastic (eg wood & fingernails) with detergents & other chemical cleaning methods much preferred. Clear plastics should not be scraped at all, just one scraping session can ruin their appearance.
Aluminium is a fairly soft metal. It tends to become pitted in use, and loss of shine on such surfaces is a non-issue.
Linished aluminium has very shallow scratch marks in precise alignment, and rearranging the pattern ruins the visual effect. Such decorative surfaces should not be scraped other than with something much softer, ie a plastic scraper. Scrape in accurate alignment with the existing marks, as scratches can occur.
Polished aluminium should not be scraped at all. Any scraping can be expected to visibly affect the surface. Chemical methods should be used. In principle aluminium can be refinished after scraping, but such refinishing isn't normally worthwhile.
May be scraped with aluminium or copper, or softer plastic scrapers. Scraping with steel is ok where a fine finish isn't needed, but it ruins the finish on stainless steel splashbacks, polished cutlery etc. Copper scourers are a good general purpose cleaning scraper for steel.
Plastic coated sinks
Chrome can be scraped with a copper scourer. Steel scourers ruin the finish.
- good where a fine surface finish doesn't matter
- available in various blade shapes for removing paint from wood.
- 5.5 mohs
- tends to cause rust staining where stored
- splinters are a problem
- too hard for almost all modern surfaces
- May be used with paint strippers
- 4-5 mohs
Stainless steel scourer
- too hard for most modern surfaces
- too weak a structure to get much pressure on the edges
- 5.5 mohs
- good for cleaning steel
- can also be used for exfoliation
- copper has some antibacterial effect
- removes rust spots from steel
- 3-3.5 mohs
- The softest of all scrapers.
- Useful for general purpose cleaning
- When using scrap material, use only thermoplastics (flexible plastics).
- 2.5 mohs, a fairly soft scraper
- always to hand
- of limited use
- soft scraper
- removes weaker/softer forms of dirt
- aka pan scrapers
- always to hand: a cut edge on some plastic kitchen waste works if you run out
- 2.5-3 mohs, softer than copper
- Useful for surfaces that won't tolerate anything harder
- Good for removing paint from glass
- the scraping edge soon wears in use
- Pieces from an ali drinks can cut out with scissors work well
- When using drinks can ali, it self sharpens as it wears
Ad hoc scrapers
Plastic: expired credit card, offcut of thermoplastic (eg from kitchen bin)
Aluminium: offcut of sheet material.
Power scrapers use a vibrating metal blade. Combination sander/scrapers are available.
About shave hooks
Shave hooks are often sold blunt, and often not even with the edge properly ground to shape. In this condition they're very ineffective, and need grinding and sharpening to be useful.